Ensure KEYSTORE environment variable exists before attempting to read it as the keystore file
Ensure KEYSTORE environment variable exists before attempting to read it as the keystore file

This allows other developers to checkout the project and build it successfully even if they do not have the KEYSTORE set up properly to build a release build (something they wouldn't do anyways).

ianhanniballake/ContractionTimer,ianhanniballake/ContractionTimer