Add missing dot (#3273)

Author: AlexanderLukin

public/docs/ts/latest/guide/testing.jade

@@ -1399,7 +1399,7 @@ a#stub-component
   The test setup should look familiar
 +makeExample('testing/ts/src/app/app.component.spec.ts', 'setup-stubs', 'src/app/app.component.spec.ts (Stub Setup)')(format='.')
 :marked
-  The `AppComponent` is the declared test subject 
+  The `AppComponent` is the declared test subject.
   The setup extends the default testing module with one real component (`BannerComponent`) and several stubs.
 
   * `BannerComponent` is simple and harmless to use as is.