docs(testing): change createInstance to createComponent (#2475)

Author: Foxandxss

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

@@ -880,7 +880,7 @@ a(href="#top").to-top Back to top
   :marked
     Do not configure the `TestBed` after calling `compileComponents`. 
     Make `compileComponents` the last step 
-    before calling `TestBed.createInstance` to instantiate the _component-under-test_.
+    before calling `TestBed.createComponent` to instantiate the _component-under-test_.
 :marked
   The `DashboardHeroComponent` spec follows the asynchonous `beforeEach` with a
   _synchronous_ `beforeEach` that completes the setup steps and runs tests ... as described in the next section.