title: Update just one gem with bundler
body: <p>I use bundler to manage dependencies in my rails app, and I have a gem hosted in a git repository included as followed:</p>
  
  <pre><code>gem 'gem-name', :git =&gt; 'path/to/my/gem.git'
  </code></pre>
  
  <p>To update this gem, I execute <code>bundle update</code> but it also updates all the gem mentioned in Gemfile. So what is the command to update just one specific gem?</p>