add dep tslib

[milahu]

tslib is required for 'npm run build'

> rollup -c rollup.config.js

src/remapping.ts → dist...
[!] (plugin typescript) Error: @rollup/plugin-typescript TS2354: This syntax requires an imported helper but module 'tslib' cannot be found.

currently, tslib is only in package-lock.json but not in package.json

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[milahu]

@googlebot I signed it!
what would this world be without lawyers? of course, nothing!

[jridgewell]

Thanks for pointing this out!