Upgrade spymemcached to 2.10.4

Change-Id: Id2ba05399a89c348eda22afd57f3dfda42d0ceae
Reviewed-on: http://review.couchbase.org/31733
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>