docs($injector): fix syntax error

There was a missing parenthesis in $injector test example

Closes #9469

src/auto/injector.js

@@ -115,7 +115,7 @@ function annotate(fn) {
  *   expect($injector.get('$injector')).toBe($injector);
  *   expect($injector.invoke(function($injector){
  *     return $injector;
- *   }).toBe($injector);
+ *   })).toBe($injector);
  * ```
  *
  * # Injection Function Annotation