title: rbenv: gem commands are not found on Linux Mint
body: <p>I'm on Linux Mint 17.2.
  I recently removed ruby with <code>apt-get purge ruby</code>.</p>
  
  <p>I then installed <code>rbenv</code> and then did <code>rbenv install 2.3.0</code> so now, <code>~/.rbenv/versions/2.3.0/bin/ruby</code> exists.</p>
  
  <p>But now, I can't do <code>gem install rubocop</code>. I get this:</p>
  
  <pre><code>$ gem install rubocop
  rbenv: gem: command not found
  
  The `gem' command exists in these Ruby versions:
    2.3.0
  </code></pre>
  
  <p>But I can do <code>~/.rbenv/versions/2.3.0/bin/gem install rubocop</code>.
  However, once I'm done, I can't use it:</p>
  
  <pre><code>$ rubocop --auto-correct
  -bash: /usr/local/bin/rubocop: /usr/bin/ruby1.9.1: bad interpreter: No such file or directory
  </code></pre>
  
  <p>I also can't find out where this ruby came from:</p>
  
  <pre><code>$ dpkg -S /usr/bin/ruby1.9.1
  dpkg-query: no path found matching pattern /usr/bin/ruby1.9.1
  </code></pre>
  
  <p>It's possible it was installed via RVM a long time ago.</p>
  
  <p>Any idea how I can fix my Ruby?</p>