Q:

Heroku deployment failing after making requirements.txt file

I have a flask application, that I want to push to Heroku, but is failing. I get the error: 
 Requested runtime (python-3.5.1) is not available for this stack

I looked into my runtime.txt file:
python-3.6.5

which seems to be the right version of python.
in my requirements.txt I have this:
Flask==0.12.0
Jinja2==2.8.1
gunicorn==19.6.0

I only use Flask and Jinja so far.
How come I still get this error 

A:

Make sure you commit your changes in your dependency files before you push to Heroku.

