docs(reactive-forms): fix import symbol typos (#3368)

Author: joseph-newton

public/docs/ts/latest/guide/reactive-forms.jade

@@ -715,7 +715,7 @@ a#set-data
   hook, which Angular calls whenever the input `hero` property changes
   as the following steps demonstrate.
 
-  First, import the `ngOnChanges` and `import` symbol in `hero-detail.component.ts`.
+  First, import the `OnChanges` and `Input` symbols in `hero-detail.component.ts`.
 
 +makeExample('reactive-forms/ts/src/app/hero-detail-6.component.ts', 'import-input','src/app/hero-detail.component.ts (core imports)')(format=".")