COMPAT: Matplotlib 2.2 compatability
Summary of changes

- clean up version detection in compat
- Update timedelta tick formatting tests. Matplotlib fixed tick formatting of timedeltas so they're consistent with non-timedelta formatting.

closes #20031 
Hello @TomAugspurger! Thanks for updating the PR.







Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 12, 2018 at 15:27 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20079?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@bfe6ebc`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `90%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20079/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20079?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20079   +/-   ##
=========================================
  Coverage          ?   91.73%           
=========================================
  Files             ?      150           
  Lines             ?    49139           
  Branches          ?        0           
=========================================
  Hits              ?    45078           
  Misses            ?     4061           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.11% <90%> (?)` | |
| #single | `41.9% <75%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20079?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_compat.py](https://codecov.io/gh/pandas-dev/pandas/pull/20079/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb21wYXQucHk=) | `90.9% <90%> (ø)` | |

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[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20079?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/20079?src=pr&el=footer). Last update [bfe6ebc...ef0d6ad](https://codecov.io/gh/pandas-dev/pandas/pull/20079?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 This should be good to go. thanks!