Land rapid7#4454 - Fix duplicate :ua_maxver key in firefox exploit

Author: wchen-r7

modules/exploits/multi/browser/firefox_webidl_injection.rb

@@ -15,7 +15,7 @@ class Metasploit3 < Msf::Exploit::Remote
 
   autopwn_info({
     :ua_name    => HttpClients::FF,
-    :ua_maxver  => "22.0",
+    :ua_minver  => "22.0",
     :ua_maxver  => "27.0",
     :javascript => true,
     :rank       => ExcellentRanking