express middleware: bump version

Author: timsuchanek

packages/graphql-playground-middleware-express/package.json

@@ -14,7 +14,7 @@
   "files": [
     "dist"
   ],
-  "playgroundVersion": "1.5.13",
+  "playgroundVersion": "1.6.6",
   "scripts": {
     "build": "rimraf dist && tsc",
     "prepare": "npm run build"