title: `bundle install` saves parameters in the config file, can it be prevented?
body: <p>Documentation for <code>bundle config</code> says that a configuration file is necessary for remembering options such as <code>--path</code> or <code>--without</code>.</p>
  
  <p>I find that when I run <code>bundle install --without some-group</code> or <code>BUNDLE_WITHOUT=some-group bundle install</code>, my <code>.bundle/config</code> file has a new line, namely:</p>
  
  <pre><code>BUNDLE_WITHOUT: "some-group"
  </code></pre>
  
  <p>I would like be able to install without a certain group yet not have a new line in <code>.bundle/config</code>.</p>
  
  <p>This is inconvenient because <code>.bundle/config</code> is naturally under source control, but I have two development environments, one where <code>some-group</code> can be installed and one where it can't.</p>
  
  <p>I don't want developers to see untracked modifications in their git status when they develop in the platform where an environment variable <code>BUNDLE_WITHOUT</code> is set.</p>
  
  <p>Recommendations?</p>