docs($injector): use square bracket notation for $inject annotation

Closes #5104

src/auto/injector.js

@@ -221,7 +221,7 @@ function annotate(fn) {
  *     // ...
  *   }
  *   // Define function dependencies
- *   MyController.$inject = ['$scope', '$route'];
+ *   MyController['$inject'] = ['$scope', '$route'];
  *
  *   // Then
  *   expect(injector.annotate(MyController)).toEqual(['$scope', '$route']);