Add tests ensuring minimum eslint peer dependency version is compatible with our rules

[lshearer]

We specify eslint as a peer dependency of eslint-config-hudl, but there are a few issues:

• The version in peerDependencies differs from that in devDependencies, so the version tests are run with does not fall in the same version range.
• There is no maximum version currently on the peer dependency
• The dev dependency uses ^, so it will install the latest compatible. We should be testing against the earliest.

Solution:

• Change the peer dependency to have a max value (or use ^ form)
• Set the dev dependency to be exactly equal to the minimum version satisfying the peer dependency
• Add tests to ensure these values stay in sync