docs: make tests work without changing height of view.

Author: chriskrycho

tests/dummy/app/templates/application.hbs

@@ -1,6 +1,6 @@
 {{outlet}}
 
-<div style='visibility: hidden'>
+<div style='visibility: hidden; height: 0'>
 {{!--
   Unlike the rest of this document, these two components are used as part of the
   addon's test suite. As such, they need to be rendered. However, they must not