docs(guide/Dependency Injection): fix angular.injector arguments list
docs(guide/Dependency Injection): fix angular.injector arguments list

The original file included a code sample using `angular.injector(['myModule', 'ng'])`,
which appears to be incorrect when trying to retrieve anything attached to `myModule`.
Reversing the args fixes this.

Closes #12292

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js