Fixed 6 more warnings from Android Lint: removed hardcoded text from the menu.

Run lint --quiet --check HardcodedText . to find these texts.
Revised the travis configuration to use the latest version of build tools.

Notes:
  - The format needs to include the major, minor and micro version i.e. 18.1.0 not just 18.1
  - I found the details in https://dl-ssl.google.com/android/repository/repository-8.xml
  - remember to use android list sdk to obtain the human-readable set of uninstalled packages.