Deal with breaking changes from MDN compat DB

[robatwilliams]

They have a non-traditional SemVer policy, which includes releasing breaking changes as minor and patch releases.

In #60 and other upgrades I find these breaking changes, but they could happen to package users any time, because we don't depend on a fixed patch version (we use ^x.x.x). The user workaround would be to manually install an older version, but I can't expect that users would be able to figure out what the problem is (with the current error caused, at least).

There has been some discussion on mdn/browser-compat-data#7563 and other linked issues on their repo.

Ideas to solve:

• write a warning in the readme
• improve error handling
• pin to specific patch version
• use dependabot as suggested here Adopt better SemVer practices mdn/browser-compat-data#7563 (comment)
• MDN DB to become more normal when it comes to semver

[robatwilliams]

Dependabot will be no good as I don't want to be regularly having to release this.

Use a pinned version and let people use package.json:overrides if they need newer data