Bump version to v5.0.0
Bump version to v5.0.0

Change-Id: I5b4ecc70e61296638dcc7a8861815bf650420c32
Reviewed-on: http://review.couchbase.org/75899
Reviewed-by: Mark Nunberg <dab05a0fe859c5cb93882b2a75a0d613501b07be@couchbase.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/gocbcore