Remove trailing whitespace from examples Makefile

Summary:
The Makefile in the examples directory contained an empty line contain a tab character. This made my Emacs ask on every save `Suspicious line 10. Save anyway? (y or n)`
Closes https://github.com/facebook/rocksdb/pull/1872

Differential Revision: D4573881

Pulled By: siying

fbshipit-source-id: fb3b4ee