title: Overriding configuration with environment variables in typesafe config
body: <p>Using <a href="https://github.com/typesafehub/config" rel="noreferrer">typesafe config</a>, how do I override the reference configuration with an environment variable? For example, lets say I have the following configuration:</p>
  
  <pre><code>foo: "bar"
  </code></pre>
  
  <p>I want it to be overriden with the environment variable <code>FOO</code> if one exists.</p>