fix(deps): use new middleware

Author: schickling

Diff for: package.json

@@ -46,7 +46,7 @@
     "express": "^4.16.2",
     "graphql": "^0.12.0",
     "graphql-import": "^0.3.0",
-    "graphql-playground-middleware-express": "1.4.7",
+    "graphql-playground-middleware-express": "1.4.8",
     "graphql-playground-middleware-lambda": "1.3.9",
     "graphql-subscriptions": "^0.5.6",
     "graphql-tools": "^2.16.0",