message: Fix Component names in usage example
  Closes:
diff: @@ -186,9 +186,9 @@ class CustomGraphiQL extends React.Component {
  />
  // Some other possible toolbar items
  - <GraphiQL.Toolbar.Menu title="File">
  - <GraphiQL.Toolbar.MenuItem title="Save" onClick={...}>
  - <GraphiQL.Toolbar.Menu>
  + <GraphiQL.Menu title="File">
  + <GraphiQL.MenuItem title="Save" onClick={...}>
  + </GraphiQL.Menu>
  <OtherReactComponent someProps="true" />
  