fix Flow typings for flow() - mobx4

[vonovak]

same as #2164 for mobx 4

[danielkcz]

Thanks!

[vovkasm]

With mobx 4.15.0 I have this error now:

node_modules/mobx/lib/api/flow.d.ts:9:108 - error TS2304: Cannot find name 'AsyncGenerator'.

9 export declare function flow<R, Args extends any[]>(generator: (...args: Args) => Generator<any, R, any> | AsyncGenerator<any, R, any>): (...args: Args) => CancellablePromise<R>;
                                                                                                             ~~~~~~~~~~~~~~


Found 1 error.

npm ERR! Test failed.  See above for more details.

Downgrade to 4.14.1 fixed the problem.

[vovkasm]

@vonovak Above error because AsyncGenerator defined only in lib.es2018.asyncgenerator.d.ts

@FredyC Does this mean that mobx (even 4.x) can be used only with "lib": ["es2018"] in tsconfig?

[danielkcz]

You are commenting on the wrong PR, this is about FlowType. Please open the new issue instead.

There is a requirement to use TS 3.6 since the last release. Not sure about lib, that might wrong.

[vovkasm]

Thank you! And sorry, not understand that this about flowtype. Just found this ticket with search. Will create distinct bug report.