Tweet only about first-timer-only issues again.
Tweet only about first-timer-only issues again.

This rolls back the change which enabled tweets for labels beginners,
up-for-grabs, etc. It was decided that we'd rather have quality of only
'first-timers-only' labels rather than the quantity of other labels.

See discussion on the PR #3.

musically-ut/first-timers-only-bot,musically-ut/first-timers-only-bot