Allow tslib v2 as peer dep

[huozhi]

I'm upgrading typescript-eslint with typescript v4, but the tslib under tsutils is always installed as 1.x which is unable to work with typescript v4.3. Array spreading syntax is broken while building.

error messgae

This syntax requires an imported helper named '__spreadArray' which does not exist in 'tslib'. Consider upgrading your version of 'tslib'`

[jbrower2]

@ajafff Can this be merged? This would make my PR unnecessary, and fix many people's issues.