travis: Update which directories are cached
travis: Update which directories are cached

See also:
https://docs.travis-ci.com/user/languages/android/#Caching

Signed-off-by: Greg Meiste <8a8f45e57c045ec63dc7e56e5eda862ea8c7cd4f@gmail.com>

meisteg/RaspberryPiTempAlarm,meisteg/RaspberryPiTempAlarm,meisteg/RaspberryPiTempAlarm