Version 12.x depends on TypeScript 3+ consumers ?

[RustyF]

I spent a while trying to work out why an Angular 5 app couldn't use 12.x but it was due to the package using a recent TypeScript (4?) and generating d.ts files only compatible with TypeScript 3+ (Angular 5 only uses 2.x). I used 11.x in the end but I wanted to make this dependency explicit for others.

I was going to PR a change to add "typescript": ">=3" to the dependencies but I'm sure not if this is the correct way?