Fix grammar in proxy_except description

Remove trailing preposition.

lib/plugins/config/lang/en/lang.php

@@ -181,7 +181,7 @@ $lang['proxy____port']    = 'Proxy port';
 $lang['proxy____user']    = 'Proxy user name';
 $lang['proxy____pass']    = 'Proxy password';
 $lang['proxy____ssl']     = 'Use SSL to connect to proxy';
-$lang['proxy____except']  = 'Regular expression to match URLs for which the proxy should be skipped for.';
+$lang['proxy____except']  = 'Regular expression to match URLs for which the proxy should be skipped.';
 
 /* Safemode Hack */
 $lang['safemodehack'] = 'Enable safemode hack';