hide protolude redifined imports

[marcosh]

attempt to solve #150

[jml]

Thanks for tackling this, @marcosh

This change introduces build warnings for users of protolude 0.2.0. I would rather not have the warnings, and think the right thing to do is restrict graphql-api to use protolude 0.2.1 and later.

Concretely, this means:

• [ ] Add a note to the $next release section of CHANGELOG.rst about the changed protolude requirements
• [ ] Update package.yaml to depend on protolude >= 0.2.1
• [ ] Update stack.yaml to say protolude-0.2.1 rather than protolude-0.2 (not 100% sure this is necessary)

@marcosh, are you OK to make these changes?

Separately, we should do a follow-up PR that breaks the build on warnings.

[marcosh]

@jml I updated the PR, hope everything's fine