Remove the yarn engine check from package.json or relax it

[mgol]

Some time ago npm has removed support for "engineStrict": true in package.json and what you put in engines in package.json is purely advisory. Unfortunately, yarn went in a opposite direction and actually enforces the check unless you pass it the --ignore-engines flag. This means people with the latest stable yarn installed are unable to build angular@ which depends on dgeni-packages until they learn about this flag. Moreover, Angular invokes yarn at the beginning of the build so if someone has incorrect dependencies, their build will break.

That's why I think we have to stop using the engines field of package.json (at least for yarn) and do it in a different way. :/