PYCBC-252: Removed the trailing full stop.

Removed the trailing full stop from the error message as we append
the source code that triggered the error.

Change-Id: Id6c0129785904b612f9caa8be9351f5bce9f0c59
Reviewed-on: http://review.couchbase.org/39447
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>