Well, nano -l is much easier way to find right line and fix it right away 
If you haven’t change too much app.yml line 9 is just before templates: — can there be something strange as extra whitespace?
But one thing I’ve learned about YAML is there can be a whitespace almost anywhere, missing space, missing quote or wrong type - and error is pointing to wrong place.
I would say it is easier delete app.yml and do setup again.