Fix issue where TypeScript errors in scripts/ folder weren't picked up

Summary: This diff fixes an issue where the `scripts` folder wasn't automatically type checked by TypeScript, and as a result `yarn flipper-server` was broken atm.

Reviewed By: nikoant

Differential Revision: D33348825

fbshipit-source-id: 059a834cacb881d45ae4b0933af3f1feabb90182

desktop/scripts/jest-setup.ts

@@ -9,7 +9,7 @@
 
 // import/no-unresolved complains, although it is a perfectly fine import
 // eslint-disable-next-line
-global.fetch = require('jest-fetch-mock');
+(global as any).fetch = require('jest-fetch-mock');
 
 // @ts-ignore
 global.electronRequire = require;