Fixes truncated error message "C extension: umpy.core.multiarray failed to import"
This occurred because lstrip is the wrong tool here:
```
>>> e = 'cannot import name numpy.core.multiarray'
>>> str(e).lstrip('cannot import name ')
'umpy.core.multiarray'
```
Better:
```
>>> str(e).replace('cannot import name ', '')
'numpy.core.multiarray'
```
--

 - [ ] closes #xxxx
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [ ] whatsnew entry

can you post a minimal example that repros the incorrect message? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=h1) Report
> Merging [#16366](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d92f06a06fe45f99cbc8a813f4128447f9466aa5?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16366/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16366      +/-   ##
==========================================
- Coverage   90.38%   90.36%   -0.02%     
==========================================
  Files         161      161              
  Lines       50916    50916              
==========================================
- Hits        46021    46011      -10     
- Misses       4895     4905      +10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.14% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.22% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.68% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.23% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=footer). Last update [d92f06a...eca0a14](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=h1) Report
> Merging [#16366](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d92f06a06fe45f99cbc8a813f4128447f9466aa5?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16366/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16366      +/-   ##
==========================================
- Coverage   90.38%   90.36%   -0.02%     
==========================================
  Files         161      161              
  Lines       50916    50916              
==========================================
- Hits        46021    46011      -10     
- Misses       4895     4905      +10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.14% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.22% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.68% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.23% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=footer). Last update [d92f06a...eca0a14](https://codecov.io/gh/pandas-dev/pandas/pull/16366?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Here's how I can reproduce it - by installing pandas 0.18 on my OSX (latest). I don't know why I get the error - I don't have pandas or numpy installed in the system-wide python or anything. I don't get the error message with pandas 0.21.1. But the actual error is by the by, as no doubt there are a few ways this can crop up.

```
dread@dmbp:~$ cd /tmp
dread@dmbp:/tmp$ virtualenv test
Running virtualenv with interpreter /usr/local/bin/python3
Using base prefix '/usr/local/Cellar/python3/3.6.0_1/Frameworks/Python.framework/Versions/3.6'
New python executable in /private/tmp/test/bin/python3.6
Also creating executable in /private/tmp/test/bin/python
Installing setuptools, pip, wheel...done.
dread@dmbp:/tmp$ . /private/tmp/test/bin/activate
(test) dread@dmbp:/tmp$ pip install pandas==0.18
Collecting pandas==0.18
Collecting python-dateutil>=2 (from pandas==0.18)
  Using cached python_dateutil-2.6.0-py2.py3-none-any.whl
Collecting numpy>=1.7.0 (from pandas==0.18)
  Using cached numpy-1.12.1-cp36-cp36m-macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.macosx_10_10_intel.macosx_10_10_x86_64.whl
Collecting pytz>=2011k (from pandas==0.18)
  Using cached pytz-2017.2-py2.py3-none-any.whl
Requirement already satisfied: six>=1.5 in ./test/lib/python3.6/site-packages (from python-dateutil>=2->pandas==0.18)
Installing collected packages: python-dateutil, numpy, pytz, pandas
Successfully installed numpy-1.12.1 pandas-0.18.0 python-dateutil-2.6.0 pytz-2017.2
(test) dread@dmbp:/tmp$ python -c 'import pandas'
RuntimeError: module compiled against API version 0xb but this version of numpy is 0xa
Traceback (most recent call last):
  File "/private/tmp/test/lib/python3.6/site-packages/pandas/__init__.py", line 25, in <module>
    from pandas import hashtable, tslib, lib
ImportError: numpy.core.multiarray failed to import

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/private/tmp/test/lib/python3.6/site-packages/pandas/__init__.py", line 31, in <module>
    "extensions first.".format(module))
ImportError: C extension: umpy.core.multiarray failed to import not built. If you want to import pandas from the source directory, you may need to run 'python setup.py build_ext --inplace' to build the C extensions first.
``` thanks!