[Search] Fix mutation.listen

Update mutation.listen to match previous variable
names changes related to nasa/openmctweb#141.

platform/core/src/capabilities/MutationCapability.js

@@ -171,7 +171,7 @@ define(
          * @memberof platform/core.MutationCapability#
          */
         MutationCapability.prototype.listen = function (listener) {
-            return this.mutationTopic.listen(listener);
+            return this.specificMutationTopic.listen(listener);
         };
 
         /**