DOC/BLD: pin IPython version to 4.2.0 (#13639)
xref #13639

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13647?src=pr) is **84.38%**

> Merging [#13647](https://codecov.io/gh/pydata/pandas/pull/13647?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13647   diff @@
==========================================
  Files           142        142          
  Lines         51225      51225          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43225      43225          
  Misses         8000       8000          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [20de266...de50772](https://codecov.io/gh/pydata/pandas/compare/20de2661c8eff66e465248cbe28062eae0e0e3bb...de50772e050d3e860bd82d65cbb08edcf8538f4e?src=pr)
 Now it works
