Don't error if regex syntax is invalid for ~ default.

modules/command.js

@@ -69,10 +69,12 @@ var command = function(dbot) {
                         dbot.commands[commandName](event);
                         dbot.save();
                     } else {
+                        if(commandName !== '~') {
                             event.reply(dbot.t('syntax_error'));
                         }
                     }
                 }
+            }
         },
 
         'on': 'PRIVMSG',