Bump version to v8.0.0-alpha.4
Bump version to v8.0.0-alpha.4

Change-Id: I02f2c8b18e1f00b202a0a08f7d36b6587d4230d8
Reviewed-on: http://review.couchbase.org/112493
Reviewed-by: Graham Pople <b547cf3375d94c7a5ef544588e5143e8c9349f5c@gmail.com>
Tested-by: Charles Dixon <e13bf4498b4994e133fd3586350658dc4a59329a@gmail.com>

brett19/gocbcore