Update graphql in Docker image to fix --sort-export
v4.12.3

One or the other sorts ignoring case, while the other does not.

Verify by running in a Linux container on Windows versus postgraphile installed locally via yarn.

This will come up a lot in CI scenarios as long as any of the developers use Windows and check in code.

You must modify your `package.json` to require `graphql` greater than or equal to `v15.5.0` to include the fix or backport it by copying the fix in `graphql` to `postgraphile`