s/PortabilityTimeTest.cpp/TimeTest.cpp
s/PortabilityTimeTest.cpp/TimeTest.cpp

Summary:
The test file in `../portability/test` is named `TimeTest.cpp`. Makefile refers to it as `PortabilityTimeTest.cpp`. Possibly a typo. Or the test file should be renamed to `PortabilityTimeTest.cpp`.
Closes https://github.com/facebook/folly/pull/438

Reviewed By: yfeldblum

Differential Revision: D3558452

Pulled By: Orvid

fbshipit-source-id: 0cee874b63e98e671153c507f42a7a3b9d8084c1

mqeizi/folly,rklabs/folly,Orvid/folly,floxard/folly,facebook/folly,facebook/folly,floxard/folly,mqeizi/folly,rklabs/folly,Orvid/folly,floxard/folly,charsyam/folly,rklabs/folly,facebook/folly,mqeizi/folly,mqeizi/folly,Orvid/folly,mqeizi/folly,Orvid/folly,charsyam/folly,rklabs/folly,facebook/folly,floxard/folly,floxard/folly,charsyam/folly,Orvid/folly,facebook/folly,charsyam/folly,rklabs/folly