title: Correct .env file with serverless-dotenv-plugin
body: <p>I'm using the following as a custom <code>serverless-dotenv-plugin</code> plugin configuration:</p>
  
  <p><code>
  custom:
    dotenv:
      path: .env-${opt:stage, 'local'}
  </code></p>
  
  <p>But what I'm really trying to get is that the environment be loaded from <code>.env</code> file when I give no arguments and <code>.env.staging</code> file when I use <code>staging</code> as a CLI argument.</p>
  
  <p>I don't know how this can be reflected in <code>path</code> above. Any help please?</p>