CI: move clipboard tests to an allowed-failure test
CI: change 2.7-build_test -> 3.6-build_test
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=h1) Report
> Merging [#18251](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9e3ad63cdb030c6b369d9d822469bb968e2d1804?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/18251/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18251      +/-   ##
==========================================
- Coverage   91.43%   91.41%   -0.02%     
==========================================
  Files         164      164              
  Lines       50090    50090              
==========================================
- Hits        45798    45789       -9     
- Misses       4292     4301       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.22% <ø> (ø)` | :arrow_up: |
| #single | `39.52% <ø> (-0.92%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/clipboard/clipboards.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9jbGlwYm9hcmRzLnB5) | `24.05% <0%> (-2.54%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <0%> (+0.09%)` | :arrow_up: |
| [pandas/io/clipboard/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9fX2luaXRfXy5weQ==) | `76.19% <0%> (+2.38%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18251?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/18251?src=pr&el=footer). Last update [9e3ad63...35cafbd](https://codecov.io/gh/pandas-dev/pandas/pull/18251?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/18251?src=pr&el=h1) Report
> Merging [#18251](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9e3ad63cdb030c6b369d9d822469bb968e2d1804?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18251/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18251      +/-   ##
==========================================
- Coverage   91.43%   91.39%   -0.05%     
==========================================
  Files         164      164              
  Lines       50090    50096       +6     
==========================================
- Hits        45798    45783      -15     
- Misses       4292     4313      +21
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.2% <ø> (-0.02%)` | :arrow_down: |
| #single | `39.52% <ø> (-0.92%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/clipboard/clipboards.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9jbGlwYm9hcmRzLnB5) | `24.05% <0%> (-2.54%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.38% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `92.03% <0%> (ø)` | :arrow_up: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `91.07% <0%> (+0.01%)` | :arrow_up: |
| [pandas/core/computation/eval.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vZXZhbC5weQ==) | `97.11% <0%> (+0.08%)` | :arrow_up: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <0%> (+0.09%)` | :arrow_up: |
| [pandas/io/clipboard/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=tree#diff-cGFuZGFzL2lvL2NsaXBib2FyZC9fX2luaXRfXy5weQ==) | `76.19% <0%> (+2.38%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18251?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/18251?src=pr&el=footer). Last update [9e3ad63...35cafbd](https://codecov.io/gh/pandas-dev/pandas/pull/18251?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
