Update GraphiQL to latest version - POST Request is not Spec conform

[glucaci]

This is how the POST Request payload should look like:

{
  "query": "...",
  "operationName": "...",
  "variables": { "myVariable": "someValue", ... }
}

In the version of graphiql that is used the "variables" are warped in a string like this

"variables": "{ "myVariable": "someValue", ... }"

In the last version of graphiql this is fixed.