fix(guide/form): fix a typo (#2483)

Author: alirezamirian

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

@@ -208,7 +208,7 @@ code-example(format="").
 :marked
 .l-sub-section
   :marked
-    There is only one changes:
+    There is only one change:
 
     1. The `template` is simply the new element tag identified by the component's `selector` property.
     This will display the hero form when the application component is loaded.