fixed jsonGraphqlExpress import

Author: sehmaschine

README.md

@@ -398,7 +398,7 @@ Then use the `jsonGraphqlExpress` express middleware:
 
 ```js
 import express from 'express';
-import { jsonGraphqlExpress } from 'json-graphql-server';
+import jsonGraphqlExpress from 'json-graphql-server';
 
 const PORT = 3000;
 const app = express();
@@ -515,7 +515,7 @@ fetch({
 
 ```js
 import express from 'express';
-import { jsonGraphqlExpress } from 'json-graphql-server';
+import jsonGraphqlExpress from 'json-graphql-server';
 
 import OAuthSecurityMiddleWare from './path/to/OAuthSecurityMiddleWare';