title: Heroku push rake assets fail suddenly using precompile
body: <p>I get an error when I do a 'git push heroku master'.<br>
  I compile assets locally using:</p>
  
  <pre><code>rake assets:precompile RAILS_ENV=production --trace
  </code></pre>
  
  <p>The thing is, this has been working regularly over the last few months and only yesterday did something decide to fail.</p>
  
  <p>I also tried the following to recompile from scratch with same result:</p>
  
  <pre><code>rake assets:clobber --trace
  rake assets:precompile RAILS_ENV=production --trace
  </code></pre>
  
  <p>Not sure how to debug this. My most recent check-in looks reasonable (i.e. I was not editing configuration files or rakefile etc.).  I was changing some png images alright (new images, resizing images) but precompiling locally does not seem to show any errors.</p>
  
  <p>Here is the start of the error message.</p>
  
  <pre><code>remote: -----&gt; Detecting rails configuration
  remote: -----&gt; Detecting rake tasks
  remote:
  remote:  !
  remote:  !     Could not detect rake tasks
  remote:  !     ensure you can run `$ bundle exec rake -P` against your app
  remote:  !     and using the production group of your Gemfile.
  remote:  !     /tmp/build_a612be38eac01922e9ad7a0a8c37a351/vendor/bundle/ruby/2.2.0/gems/autoprefixer-rails-9.4.10/lib/autoprefixer-rails/processor.rb:83: warning: else without rescue is useless
  remote:  !     rake aborted!
  remote:  !     SyntaxError: /tmp/build_a612be38eac01922e9ad7a0a8c37a351/vendor/bundle/ruby/2.2.0/gems/autoprefixer-rails-9.4.10/lib/autoprefixer-rails/processor.rb:79: syntax error, unexpected '.'
  remote:  !     from ||= if defined? Rails&amp;.respond_to?(:root) &amp;&amp; Rails&amp;.root
  remote:  !     ^
  remote:  !     /tmp/build_a612be38eac01922e9ad7a0a8c37a351/vendor/bundle/ruby/2.2.0/gems/autoprefixer-rails-9.4.10/lib/autoprefixer-rails/processor.rb:79: syntax error, unexpected '.'
  remote:  !     from ||= if defined? Rails&amp;.respond_to?(:root) &amp;&amp; Rails&amp;.root
  remote:  !     ^
  </code></pre>