change search instrumentation field s/limit/size/

matches up with how `time` param works. @mtodd you okay with this?

Author: Jerry Cheung

lib/net/ldap/connection.rb

@@ -381,7 +381,7 @@ def search(args = nil)
                filter:     filter,
                base:       base,
                scope:      scope,
-               limit:      size,
+               size:       size,
                time:       time,
                sort:       sort,
                referrals:  refs,