Use right side verbatim for ES6 class setter.

lib/6to5/transformation/helpers/replace-supers.js

@@ -48,7 +48,7 @@ ReplaceSupers.prototype.setSuperProperty = function (property, value, isStatic,
         ]
       ),
       isComputed ? property : t.literal(property.name),
-      t.identifier(value.name),
+      value,
       thisExpression
     ]
   );

test/fixtures/esnext/es6-classes/getter-setter-super.js

@@ -26,8 +26,7 @@ class Cat extends Animal {
   }
 
   set name(val) {
-    super.name = val;
-    this._name += ' Cat';
+    super.name = val + ' Cat';
   }
 }