Add environment-aware createHash function to apollo-env

[trevor-scheer]

This is a subset of changes proposed by this PR:
#1027

This PR adds a createHash function to apollo-env which is environment aware. That is to say, it will work in both node-like and non-node environments.

This PR also uses this function from within the apollo-graphql package.

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

*Make sure changelog entries note which project(s) has been affected. See older entries for examples on what this looks like.

[abernix]

LGTM!