[ENH] pull in warning for dialect change from pandas-gbq
- [x] ~closes~ towards https://github.com/pydata/pandas-gbq/issues/195
- [x] tests added / passed (N/A)
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22557?src=pr&el=h1) Report
> Merging [#22557](https://codecov.io/gh/pandas-dev/pandas/pull/22557?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/73dd6ece3b66008eb8077098c101d0e300b1e714?src=pr&el=desc) will **decrease** coverage by `0.13%`.
> The diff coverage is `25%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22557/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22557?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22557      +/-   ##
==========================================
- Coverage   92.17%   92.03%   -0.14%     
==========================================
  Files         169      169              
  Lines       50708    50791      +83     
==========================================
+ Hits        46740    46746       +6     
- Misses       3968     4045      +77
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.44% <25%> (-0.14%)` | :arrow_down: |
| #single | `42.29% <25%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22557?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <25%> (ø)` | :arrow_up: |
| [pandas/errors/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2Vycm9ycy9fX2luaXRfXy5weQ==) | `92.3% <0%> (-7.7%)` | :arrow_down: |
| [pandas/core/dtypes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Jhc2UucHk=) | `92.68% <0%> (-7.32%)` | :arrow_down: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `88% <0%> (-6.25%)` | :arrow_down: |
| [pandas/io/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2h0bWwucHk=) | `89.17% <0%> (-2.08%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `88.81% <0%> (-1.87%)` | :arrow_down: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `94.02% <0%> (-1.75%)` | :arrow_down: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `95.52% <0%> (-1.3%)` | :arrow_down: |
| [pandas/io/parquet.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnF1ZXQucHk=) | `71.79% <0%> (-1.25%)` | :arrow_down: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `96.92% <0%> (-0.69%)` | :arrow_down: |
| ... and [25 more](https://codecov.io/gh/pandas-dev/pandas/pull/22557/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22557?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/22557?src=pr&el=footer). Last update [73dd6ec...0de8d22](https://codecov.io/gh/pandas-dev/pandas/pull/22557?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @tswast! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/io/gbq.py`](https://github.com/tswast/pandas/blob/f5c07d283a6126f8d9dc40cdbc13d7e51f771f5c/pandas/io/gbq.py) !

 - There are no PEP8 issues in the file [`pandas/tests/io/test_gbq.py`](https://github.com/tswast/pandas/blob/f5c07d283a6126f8d9dc40cdbc13d7e51f771f5c/pandas/tests/io/test_gbq.py) !

 Travis error appears to be a temporary issue with Conda downloads. https://travis-ci.org/pandas-dev/pandas/jobs/427334975

> CondaHTTPError: HTTP 504 GATEWAY TIME-OUT for url <https://conda.anaconda.org/conda-forge/linux-64/pycryptodome-3.6.6-py27h16a7912_0.tar.bz2>

Maybe retrying it would help? thanks @tswast 