spelling: representation

Author: timeless@gmail.com

docs/content/guide/migration.ngdoc

@@ -1129,7 +1129,7 @@ app. This is no longer possible within a single module.
 
 - due to [a097aa95](https://github.com/angular/angular.js/commit/a097aa95b7c78beab6d1b7d521c25f7d9d7843d9),
   `orderBy` now treats `null` values (which in JavaScript have type `object`) as having a string
-  represenation of `'null'`.
+  representation of `'null'`.
 
 
 ### Animation (`ngAnimate`)