Use more meaningful name

$' ->
$POSTMATCH

lib/droonga/plugin/handler_search.rb

@@ -15,6 +15,7 @@
 # License along with this library; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 
+require "English"
 require "tsort"
 require "groonga"
 
@@ -185,7 +186,7 @@ def parseCondition(source, expression, condition)
       def parseOrderKeys(keys)
         keys.collect do |key|
           if key =~ /^-/
-            [$', :descending]
+            [$POSTMATCH, :descending]
           else
             [key, :ascending]
           end