Heroku version not set despite following guide
<p>I am trying to push a rails 5 app to Heroku and I believe that I followed the instructions on the Heroku page:
<a href="https://devcenter.heroku.com/articles/ruby-versions" rel="nofollow">https://devcenter.heroku.com/articles/ruby-versions</a></p>

<pre><code>$ ruby --version
ruby 2.3.1p112 (2016-04-26) [x86_64-linux-gnu]

$ cat Gemfile
.....
ruby "2.3.1"

$ heroku run bash
$ env | grep PATH
PATH=/app/bin:/usr/local/bin:/usr/bin:/bin

$ git push heroku master
remote: Compressing source files... done.
remote: Building source:
remote: 
remote: -----&gt; Ruby app detected
remote: -----&gt; Compiling Ruby/Rails
remote: -----&gt; Using Ruby version: ruby-2.2.4
</code></pre>

<p>which terminates with the error:</p>

<pre><code>remote: -----&gt; Preparing app for Rails asset pipeline
remote:        Running: rake assets:precompile
remote:        rake aborted!
remote:        NoMethodError: undefined method `symbolize_keys' for #       &lt;String:0x007fac0655feb0&gt;
remote:           /tmp/build_39bfaebc9acd5a6bcb91a69f2b13c171/vendor/bundle/ruby/2.2.0/gems /railties-5.0.0.1/lib/rails/application.rb:393:in `secrets'
</code></pre>

<p>Which I guess it is because it is using 2.2 and not 2.3.</p>

<p>The version in /bin is 1.9.3 so in case it would not find any, it should use 1.9.3 and not 2.2.4.</p>

<p>The error message above was fixed with the help of spickermann. Removing the secret.yml file from git tracking allowed the app to be deployed without errors.</p>

<p>Still, the wrong Ruby version persists and Heroku even returns a warning at the end:</p>

<pre><code>remote: ###### WARNING:
remote:        You have not declared a Ruby version in your Gemfile.
remote:        To set your Ruby version add this line to your Gemfile:
remote:        ruby '2.2.4'
remote:        # See https://devcenter.heroku.com/articles/ruby-     versions for more information.
</code></pre>

<p>Any advice about what else can be done?</p>

<p>Thank you!</p>