Fix DefinitelyTyped type definitions before publishing a new version

[tkrotoff]

Problem:
Each TypeScript release breaks popular DefinitelyTyped type definitions, example with TypeScript 2.2 release:

• whatwg-fetch and isomorphic-fetch broken: @types/isomorphic-fetch duplicate definitions with typesript 2.2 DefinitelyTyped/DefinitelyTyped#14765
• lodash broken: Lodash All declarations of 'WeakMap' must have identical type parameters. DefinitelyTyped/DefinitelyTyped#14324
• probably others

Not a good developer experience

Solution:
Fix the most popular DefinitelyTyped type definitions before publishing on npm

[corbinu]

Given the issue with loads at least was that the change would break older versions of TS. Maybe if there was some sort of @next option for DefinitelyTyped that way at least we call you have updated to that version of the definition when the RC has launched. That would have made things a little easier at least.

[jaredmahan]

When can we expect isomorphic-fetch type fixes to be deployed? Waiting on this currently...

[mhegazy]

@types/[email protected] is already out and should have the fix.

[mhegazy]

For lodash, the change DefinitelyTyped/DefinitelyTyped#14662 needs to be updated and then we can merge it.

[mhegazy]

As for the original request, we used to validate against every drop of the compiler but as the size of DT grew it became harder to do that.
I agree We should be running the validation on all DT packages at least once before every release. @andy-ms is updating the testing system to make this doable.

[weswigham]

We do this regularly now, thanks to the @typescript-bot run dt command (not just before publish, but regularly before merge), in addition to nightly testing of DT vs the nightly TS. 😄