Bump eslint packages

It is not currently possible to bump the @typescript-eslint/eslint-plugin and @typescript-eslint/parser packages all the
way to the latest 8.0.0 version because the eslint-config-airbnb-typescript has a peer dependency on 7.x of those
packages. But it is at least possible to bump the eslint packages to 7.x, which must also be accompanied by the bump of
eslint-config-airbnb-typescript to 18.0.0.

Author: per1234