title: error while deploying diaspora on heroku Failed to install gems via Bundler
body: <p>i am trying to deploy diaspora on heroku but getting this error while deploying am using rails 4.1.8 with ruby 2.0.0 on ubuntu 14.04 I had tried <code>bundle update</code> but it doesn't worked..any solution..??</p>
  
  <pre><code>&gt; ahmed@ahmed-desktop:~/diaspora$ git push -u heroku heroku:master
  &gt; Counting objects: 132081, done.
  &gt; Delta compression using up to 2 threads.
  &gt; Compressing objects: 100% (29619/29619), done.
  &gt; Writing objects: 100% (132081/132081), 91.87 MiB | 163.00 KiB/s, done.
  &gt; Total 132081 (delta 101146), reused 132070 (delta 101138)
  &gt; remote: Compressing source files... done.
  &gt; remote: Building source:
  &gt; remote:
  &gt; remote: -----&gt; Deleting 6 files matching .slugignore patterns.
  &gt; remote: -----&gt; Ruby app detected
  &gt; remote: -----&gt; Compiling Ruby/Rails
  &gt; remote: -----&gt; Using Ruby version: ruby-2.0.0
  &gt; remote: -----&gt; Installing dependencies using 1.7.12
  &gt; remote:        Running: bundle install --without development:test --path
  &gt; vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
  &gt; remote:        You are trying to install in deployment mode after changing
  &gt; remote:        your Gemfile. Run `bundle install` elsewhere and add the
  &gt; remote:        updated Gemfile.lock to version control.
  &gt; remote:        You have deleted from the Gemfile:
  &gt; remote:        * mysql2 (= 0.3.16)
  &gt; remote:        Bundler Output: You are trying to install in deployment
  &gt; mode after changing
  &gt; remote:        your Gemfile. Run `bundle install` elsewhere and add the
  &gt; remote:        updated Gemfile.lock to version control.
  &gt; remote:
  &gt; remote:        You have deleted from the Gemfile:
  &gt; remote:        * mysql2 (= 0.3.16)
  &gt; remote:  !
  &gt; remote:  !     Failed to install gems via Bundler.
  &gt; remote:  !
  &gt; remote:
  &gt; remote:  !     Push rejected, failed to compile Ruby app
  &gt; remote:
  &gt; remote: Verifying deploy...
  &gt; remote:
  &gt; remote: !    Push rejected to reddodo.
  &gt; remote:
  &gt; To https://git.heroku.com/reddodo.git
  &gt;  ! [remote rejected] heroku -&gt; master (pre-receive hook declined)
  &gt; error: failed to push some refs to 'https://git.heroku.com/reddodo.git'
  </code></pre>