docs(guide/Dependency Injection): minor punctuation fixes

Closes angular#12268

Author: kadimi

docs/content/guide/di.ngdoc

@@ -163,8 +163,8 @@ someModule.controller('MyController', function($scope, greeter) {
 });
 ```
 
-Given a function the injector can infer the names of the services to inject by examining the
-function declaration and extracting the parameter names. In the above example `$scope`, and
+Given a function, the injector can infer the names of the services to inject by examining the
+function declaration and extracting the parameter names. In the above example, `$scope` and
 `greeter` are two services which need to be injected into the function.
 
 One advantage of this approach is that there's no array of names to keep in sync with the