Fix make_signature TypeError in py3
xref #17608 

- [ ] closes #xxxx
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=h1) Report
> Merging [#17609](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fedf92287d0216d54fe756829362e1d10a3fdc58?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17609/graphs/tree.svg?token=eZ4WkYLtcO&width=650&src=pr&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17609      +/-   ##
==========================================
+ Coverage   91.19%    91.2%   +<.01%     
==========================================
  Files         163      163              
  Lines       49625    49625              
==========================================
+ Hits        45257    45260       +3     
+ Misses       4368     4365       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.99% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.2% <0%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `78% <100%> (+12%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17609?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/17609?src=pr&el=footer). Last update [fedf922...7cdf3b1](https://codecov.io/gh/pandas-dev/pandas/pull/17609?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/17609?src=pr&el=h1) Report
> Merging [#17609](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fedf92287d0216d54fe756829362e1d10a3fdc58?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17609/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17609      +/-   ##
==========================================
+ Coverage   91.19%    91.2%   +<.01%     
==========================================
  Files         163      163              
  Lines       49625    49652      +27     
==========================================
+ Hits        45257    45285      +28     
+ Misses       4368     4367       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.99% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.18% <0%> (-0.08%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `78% <100%> (+12%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/excel.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2lvL2V4Y2VsLnB5) | `80.37% <0%> (-0.18%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <0%> (-0.1%)` | :arrow_down: |
| [pandas/tseries/offsets.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvb2Zmc2V0cy5weQ==) | `97% <0%> (ø)` | :arrow_up: |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `95.59% <0%> (+0.01%)` | :arrow_up: |
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.07% <0%> (+0.02%)` | :arrow_up: |
| [pandas/core/indexes/range.py](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9yYW5nZS5weQ==) | `92.83% <0%> (+0.24%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17609?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/17609?src=pr&el=footer). Last update [fedf922...943b3e1](https://codecov.io/gh/pandas-dev/pandas/pull/17609?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Travis error looks unrelated:

```
RuntimeError: module compiled against API version 0xb but this version of numpy is 0xa
Traceback (most recent call last):
  File "/home/travis/miniconda3/envs/pandas/lib/python3.6/site-packages/_pytest/config.py", line 342, in _getconftestmodules
    return self._path2confmods[path]
KeyError: local('/home/travis/build/pandas-dev/pandas/pandas')
``` lgtm ping on green. ping.  pls consider re-opening #17600, as it fixes a problem that caused this to fail silently. thanks. see my comments for #17600 