typescript should be a normal (not dev) dependency

[blittle]

The lib/index.cjs.js artifact has a direct dependency on typescript (see line 3), which means this should have a direct dependency on typescript, instead of dev dependency. The problem is manifest with the warning when using yarn2:

Error: ts-simple-type tried to access typescript, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.

[justinfagnani]

I wonder if it's intended to be a peer dependency. I'm updating TypeScript now, but not changing this yet while I figure out how things are structured...