fix for overwritten global.Promise

Author: jeysal

packages/jest-util/src/isPromise.ts

@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+// capture global.Promise before it may potentially be overwritten
+const Promise: any = global.Promise;
+
 // see ES2015 spec 25.4.4.5, https://stackoverflow.com/a/38339199
 const isPromise = (candidate: unknown): candidate is Promise<unknown> =>
   Promise.resolve(candidate) === candidate;