Bug 1446329 - Follow-up: fix lint issue. r=me DONTBUILD

common/bindings/spinbuttons.xml

@@ -86,7 +86,7 @@
 
           if (this.hasAttribute("on" + eventname)) {
             var fn = new Function("event", this.getAttribute("on" + eventname));
-            if (fn.call(this, event) == false)
+            if (!fn.call(this, event))
               cancel = true;
           }