Look in event.path first when selecting endpoint for GraphQL Playground on Lambda, and check for null

[stubailo]

See here: https://docs.aws.amazon.com/lambda/latest/dg/eventsources.html#eventsources-api-gateway-request

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[jbaxleyiii]

@stubailo looks great to me! Thanks for fixing that