1.2.0

Note: This version requires at least TS 2.8.0 (@next at the time of this release)

This fixes the type definitions for TS 2.8 since TS 2.7 regressed (microsoft/TypeScript#22771) and only conditional mapped types from 2.8 could help fixing the definitions.
This also means there is no release of immupdate that is compatible with TS 2.7