What problem does this feature solve?

It's an additional issue about #1106 Since we have removed 'tsd', I think we should delete 'tsd' info in contributing.md and package.json

What does the proposed API look like?

:>

https://cs.github.com/vuejs/core/blob/ec795bfc517266387bb21729a0b0cb4ad8256eef/.github/contributing.md#L270 https://cs.github.com/vuejs/core/blob/ec795bfc517266387bb21729a0b0cb4ad8256eef/package.json#L34