Bump version to v7.1.6
Bump version to v7.1.6

Motivation
----------
Altering the way that versions are managed so that version numbers
are bumped just after tagging rather than just before. Doing
this makes it more clear which version a change belongs to as
changes will be made against the version that will become the tag.

Change-Id: I6d203e4081cf1ab4497e3384a0cce44c97d2babc
Reviewed-on: http://review.couchbase.org/99360
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: Charles Dixon <e13bf4498b4994e133fd3586350658dc4a59329a@gmail.com>

brett19/gocbcore