title: Generate schema.json with GraphiQL or GraphQL endpoint
body: <p>I'm having issues creating a schema.json file that can be parsed with babel-relay-plugin without running into an error. Taking a look at the <a href="https://github.com/facebook/relay/blob/master/examples/todo/data/schema.json" rel="noreferrer">schema.json</a> file included in relay's example folder, I tried to copy the query in GraphiQL but I can't seem to get it right. I'm using <a href="https://github.com/Folkloreatelier/laravel-graphql" rel="noreferrer">Laravel</a> as the backend. Is this something I can accomplish through GraphiQL or sending a request to the GraphQL endpoint and saving the response?</p>
  
  <p>The error occurring when attempting to parse the schema.json file:</p>
  
  <pre><code>Cannot read property 'reduce' of undefined while parsing file: /Users/username/Sites/Homestead/Code/ineedmg-graphql/resources/assets/js/app.js
  </code></pre>
  
  <p>Last attempt using GraphiQL:</p>
  
  <pre><code>{
    __schema {
      queryType { 
        name
      },
      types {
          kind,
          name,
          description,
          fields {
              name,
              description,
              type {
                name,
                kind,
                ofType {
                  name
                  description
                }
              }
              isDeprecated,
              deprecationReason,
          },
        inputFields {
          name
          description
        }
        interfaces {
          kind
          name
          description
        },
        enumValues {
          name
          description
          isDeprecated
          deprecationReason
        }
      },
      mutationType { 
        name
      },
      directives {
        name,
        description,
        onOperation,
        onFragment,
        onField,
        args {
          name
          description
          defaultValue
        }
      }
    }
  }
  </code></pre>