Triple quote string literal descriptions cause late validation failure

[thomasmichaelwallace]

First- thanks for all the work on this ace project!

AppSync's support for the GraphQL SDL is a little out of date. Specially it doesn't support string literals (triple quote) as descriptions: aws/aws-appsync-community#38

If you use this now best practace approach with this plug-in the schema validates (because, well, it is valid!) but your deployment will fail with:

ServerlessError: An error occurred: GraphQlSchema - Schema Creation Status is FAILED with details: Failed to parse schema document - ensure it's a valid SDL-formatted document..

Luckily I was aware of this problem, so I didn't lose too much time. But I think it would be nice if this plugin either:

1. Automatically stripped triple quote string literals before deploying the stitched schema [preferred]
2. Failed validation if the schema includes triple quote string literals.

[thomasmichaelwallace]

As part of my own deployment I'm solving the problem by pre-processing (removing the offending descriptions).

I'm more than happy to fold this into a PR if you agree it's something that should be part of this plugin.

[thomasmichaelwallace]

For reference, this is what I needed to do get my schema to pass appsync's internal definition:

const conformSchema =
  (schema) => schema
    .replace(/"""[^"]*"""\n/g, '') // appsync does not support the new style descriptions
    .replace(/#.*\n/g, '') // appysnc does not support old-style # comments in enums, so remove them all
    .replace(/ *& */g, ', ') // appsync does not support the standard '&', but the "unofficial" ',' join for interfaces

[bboure]

Fixed in #340