Updated eslint to v7.

[fabianmarz]

Description

• The original gulp-eslint package hasn't been updated since 2 years therefore move to another package (which is a fork of the original one). -> See related issue
• Another possibility would have been to use npm-force-resolutions which mimics the behaviour of the Yarn resolutions and override the dependency for the gulp-eslint package instead.
• 💡 There is this accepted RFC which will add the same behaviour for declaring dependency overrides in an upcoming version.
• Additionally I fixed some breaking error if the parent package.json does not paths for tasks which are not relevant in some use cases fixes Build process fails when paths are not defined in package.json. #37.