Gatsby V5 support - graphql dependency

[finematterdave]

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Describe the bug After upgrading to Gatsby 5, which has a dependency on graphql 16, the plugin fails to load due to a dependency on version 15.

For reference, error when using v16 of graphql is TypeError: Class constructor GraphQLNonNull cannot be invoked without 'new'.

I'll try and work on this as a PR, but just to raise it incase there's already a reason it's not upto date.

To Reproduce Install Gatsby v5, with the @imgix/gatsby plugin configured, fails during build with error above

Expected behaviour Build passes as expected

[atlawrie]

Hey thanks for looking into this. We’re working on V5 support currently but we have some other things on our plate, but we’ll circle back soon when we have the bandwidth.

[finematterdave]

https://github.com/imgix/gatsby/pull/249 a basic working PR which we're using as a fork for now until your team have some capacity to look into it.

[luqven]

Merged in #259

@finematterdave, thanks again for your work on this!