title: Heroku Push Rejected - Cannot find gem multipart-post
body: <p>I finished setting up OAuth in my app, but I can't seem to push to Heroku. There is a gem dependency that was installed (and everything works locally), but Heroku rejects the push. </p>
  
  <p>I have tried deleted my .lock file, .bundle, and have tried bundle update as well. Heroku will not accept the push</p>
  
  <pre><code>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-2.5.3
  remote: -----&gt; Installing dependencies using bundler 1.15.2
  remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
  remote:        Warning: the running version of Bundler (1.15.2) is older than the version that created the lockfile (1.17.1). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
  remote:        Fetching gem metadata from https://rubygems.org/........
  remote:        Fetching version metadata from https://rubygems.org/..
  remote:        Fetching dependency metadata from https://rubygems.org/.
  remote:        Could not find multipart-post-2.0.0 in any of the sources
  remote:        Bundler Output: Warning: the running version of Bundler (1.15.2) is older than the version that created the lockfile (1.17.1). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
  remote:        Fetching gem metadata from https://rubygems.org/........
  remote:        Fetching version metadata from https://rubygems.org/..
  remote:        Fetching dependency metadata from https://rubygems.org/.
  remote:        Could not find multipart-post-2.0.0 in any of the sources
  remote:
  remote:  !
  remote:  !     Failed to install gems via Bundler.
  remote:  !
  remote:  !     Push rejected, failed to compile Ruby app.
  remote:
  remote:  !     Push failed
  </code></pre>
  
  <p>The gem is supposed to be <code>multipart-post</code> (version 2.0.0), but for some reason it is including the version as part of the gem file. Any thoughts?</p>