Upgrade spymemcached dependency for 2.8.12

Change-Id: If89ee8f3fdf4730777e768a917c7a8d401576c0b
Reviewed-on: http://review.couchbase.org/24888
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Matt Ingenthron <matt@couchbase.com>