Temporarily disable Travis deploying to Sonatype

Travis was deploying all commits (including pull request branches) to Sonatype :rage3:
Don't deploy pull-request branches to Sonatype
Make Maven deploy script work with POSIX shell.
Fix yet another POSIX shell issue.
Only push builds from master to Sonatype
Merge pull request #833 from erd/master

Only push builds from master to Sonatype