STYLE: Fix isort failure in range.py
https://travis-ci.org/pandas-dev/pandas/jobs/443300714#L2922
Hello @gfyoung! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/indexes/range.py`](https://github.com/gfyoung/pandas/blob/9952e6107ab4d3fcce11381e97abd472d983b9c3/pandas/core/indexes/range.py) !

 Passed on travis so merging to fix master. Thanks! # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23231?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@8963218`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23231/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23231?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #23231   +/-   ##
=========================================
  Coverage          ?   92.19%           
=========================================
  Files             ?      169           
  Lines             ?    50950           
  Branches          ?        0           
=========================================
  Hits              ?    46975           
  Misses            ?     3975           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.62% <100%> (?)` | |
| #single | `42.27% <100%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23231?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/range.py](https://codecov.io/gh/pandas-dev/pandas/pull/23231/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9yYW5nZS5weQ==) | `95.77% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23231?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/23231?src=pr&el=footer). Last update [8963218...9952e61](https://codecov.io/gh/pandas-dev/pandas/pull/23231?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
