the new version of pip complains for PIL because it is an extenral repo and
the checksum cannot be verified
fix pip install command for PIL
Merge pull request #122 from enthought/fix-travis-install-for-PIL

Fix pip install complaints
Merge branch 'master' into fix-qt-keycodes

* master:
  fix pip install command for PIL
  the new version of pip complains for PIL because it is an extenral repo and the checksum cannot be verified