Add GPG signing in preparation for publishing to the Maven Central Repository.
Add GPG signing in preparation for publishing to the Maven Central
Repository.

HiWong/evernote-sdk-android,artisJIANG/evernote-sdk-android,AlexBravo/evernote-sdk-android,fivef/add_to_evernote_note,evernote/evernote-sdk-android,allentcm/evernote-sdk-android