correct _removeEndTransitionListener

Author: justjake

src/CollapsableMixin.js

@@ -47,7 +47,7 @@ var CollapsableMixin = {
     var node = this.getCollapsableDOMNode();
 
     if (node) {
-      TransitionEvents.addEndEventListener(
+      TransitionEvents.removeEndEventListener(
         node,
         this.handleTransitionEnd
       );
@@ -127,4 +127,4 @@ var CollapsableMixin = {
   }
 };
 
-module.exports = CollapsableMixin;
+module.exports = CollapsableMixin;