Update xctool args to clean+build+test

Something in build #184 broke the travis CI with 'simulator
failed to start errors. Likely the Localizable.strings update.
Updating the xctool flags and forcing a clean/build/test cycle
seemed to fix the issue.
Merge pull request #101 from votinginfoproject/feature/fix-travis-build

Update xctool args to clean+build+test