message: Add getVariableEditor() and refresh()
  Closes
  This adds two new public API methods to the `<GraphiQL>` component.
  `getVariableEditor()` gets the CodeMirror instance for editing variables.
  `refresh()` will refresh all CodeMirror instances, this may be helpful after changing the size of the containing element or after making it visible for the first time.
diff: @@ -341,6 +341,26 @@ export class GraphiQL extends React.Component {
  return this.queryEditorComponent.getCodeMirror();
  }
  + /**
  + * Get the variable editor CodeMirror instance.
  + *
  + * @public
  + */
  + getVariableEditor() {
  + return this.variableEditorComponent.getCodeMirror();
  + }
  +
  + /**
  + * Refresh all CodeMirror instances.
  + *
  + * @public
  + */
  + refresh() {
  + this.queryEditorComponent.getCodeMirror().refresh();
  + this.variableEditorComponent.getCodeMirror().refresh();
  + this.resultComponent.getCodeMirror().refresh();
  + }
  +
  /**
  * Inspect the query, automatically filling in selection sets for non-leaf
  * fields which do not yet have them.
  