Add extra include to where snappy is

Change-Id: Id01c3e648fd711e9e1464e6fa773fac411cdce92
Reviewed-on: http://review.couchbase.org/35363
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>