[Fix #17] messageSubscribers should be mutable array.

Author: xhacker

quark-shell/QSHWebViewDelegate.m

@@ -417,7 +417,7 @@ - (void)subscribeMessage:(NSString *)name withCallback:(WebScriptObject *)callba
         [self.messageSubscribers[name] addObject:callback];
     }
     else {
-        self.messageSubscribers[name] = @[callback];
+        self.messageSubscribers[name] = [NSMutableArray arrayWithObject:callback];
     }
 }