Adding matplotlib to Conda dependencies (pytorch#314)

Summary:
Noticed that matplotlib was included in setup.py and required for pip, but not for conda. Adding matplotlib so both are consistent.
Pull Request resolved: pytorch#314

Reviewed By: orionr, NarineK

Differential Revision: D20295348

Pulled By: vivekmig

fbshipit-source-id: f9a4118ff808af8a60f38fce5576fe4f7a99336f

fix insights example (pytorch#102)