title: Accessing Gatsby env variables in gatsby-config
body: <p>I am new to Gatsby and am trying to access my environment variables inside of my <code>gatsby-config.js</code> file in local development. I want to be able to test this all locally.</p>
  
  <p><code>.env.development</code></p>
  
  <pre><code>GATSBY_KEY=stuffvaluehere
  </code></pre>
  
  <p><code>gatsby-config.js</code></p>
  
  <pre><code>{
    key: process.env.GATSBY_KEY,
  }
  </code></pre>
  
  <p>Whenever I run <code>gatsby develop</code> I get an error that the value is undefined. I can't tell exactly from the <a href="https://www.gatsbyjs.org/docs/environment-variables/" rel="nofollow noreferrer">docs</a> what I would need to do in order to access these variables locally before storing them in Netlify.</p>