Fix https in endpoint

Author: huv1k

packages/graphql-playground/src/components/EndpointPopup.tsx

@@ -17,7 +17,7 @@ export interface State {
 
 export default class EndpointPopup extends React.Component<Props, State> {
   checkEndpoint = throttle(() => {
-    if (this.state.endpoint.match(/^http:\/\/\w+(\.\w+)*(:[0-9]+)?\/?.*$/)) {
+    if (this.state.endpoint.match(/^https?:\/\/\w+(\.\w+)*(:[0-9]+)?\/?.*$/)) {
       fetch(this.state.endpoint, {
         method: 'post',
         headers: {