Graphiql behind a proxy is not working

[ccamel]

As a consequence of #83, graphiql seems to be no more able to access the vendor resources nor the subscriptions when behind a proxy.

For instance, one of our service is configured as such:

graphiql:
      mapping: /graphiql
      endpoint: /my-service/graphql
      enabled: true

The service is deployed through the proxy with the route http://foo.bar/my-service/. So it exposes the following endpoints:

• graphiql: http://foo.bar/my-service/graphiql
• graphql: http://foo.bar/my-service/graphql
• subscriptions: http://foo.bar/my-service/subscriptions

In that case, the resources retrieved by the browser are:

• ✅ 200: http://foo.bar/my-service/graphiql
• ❌ 404: http://foo.bar/vendor/es6-promise.auto.min.js
• ❌ 404: http://foo.bar/vendor/fetch.min.js
• ❌ 404: http://foo.bar/vendor/react.min.js
• ...
• ❌ 404: http://foo.bar/subscriptions

[jackie1in]

please release quickly