docs($location): clarify return value for path method

docs for return of path() inaccurately describe the function’s return when a value is passed in.

Closes #14544

src/ng/location.js

@@ -482,7 +482,7 @@ var locationPrototype = {
    * ```
    *
    * @param {(string|number)=} path New path
-   * @return {string} path
+   * @return {(string|object)} path if called with no parameters, or `$location` if called with a parameter
    */
   path: locationGetterSetter('$$path', function(path) {
     path = path !== null ? path.toString() : '';