Fix vim syntax highlighter

Change-Id: Id2b35c707fce0d2e371fed10b554f993be262181
Reviewed-on: http://review.couchbase.org/24263
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>