makeKeyGeneric supports $[]

makeKeyGeneric now makes any $[<identifier>] notation generic as well

lib/mongo-object.js

@@ -671,16 +671,17 @@ export default class MongoObject {
 
   /* STATIC */
 
-  /* Takes a specific string that uses mongo-style dot notation
-   * and returns a generic string equivalent. Replaces all numeric
-   * "pieces" with a dollar sign ($).
+  /* Takes a specific string that uses any mongo-style positional update
+   * dot notation and returns a generic string equivalent. Replaces all numeric
+   * positional "pieces" (e.g. '.1') or any other positional operator
+   * (e.g. '$[<identifier>]')  with a dollar sign ($).
    *
    * @param {type} name
    * @returns {String} Generic name.
    */
   static makeKeyGeneric(key) {
     if (typeof key !== 'string') return null;
-    return key.replace(/\.[0-9]+(?=\.|$)/g, '.$');
+    return key.replace(/\.([0-9]+|\$\[.*\])(?=\.|$)/g, '.$');
   }
 
   /** Takes a string representation of an object key and its value