Jest detect open handles

[zodman]

run with:

$ npx jest --detectOpenHandles
 PASS  __tests__/test.js
  ✓ works... (121 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.345 s, estimated 1 s
Ran all test suites.

Jest has detected the following 2 open handles potentially keeping Jest from exiting:

  ●  PBKDF2REQUEST

      14 |
      15 |     function getKey(salt) {
    > 16 |         return crypto.pbkdf2Sync(secret, salt, 100000, 32, 'sha512');
         |                       ^
      17 |     }
      18 |
      19 |     this.encrypt = function encrypt(value) {

      at pbkdf2Sync (index.js:16:23)
      at Cryptr.getKey [as encrypt] (index.js:27:21)
      at Object.encrypt (__tests__/test.js:8:30)


  ●  PBKDF2REQUEST

      14 |
      15 |     function getKey(salt) {
    > 16 |         return crypto.pbkdf2Sync(secret, salt, 100000, 32, 'sha512');
         |                       ^
      17 |     }
      18 |
      19 |     this.encrypt = function encrypt(value) {

      at pbkdf2Sync (index.js:16:23)
      at Cryptr.getKey [as decrypt] (index.js:49:21)
      at Object.decrypt (__tests__/test.js:9:30)

I understand the jest don't finish correctly because something it's maintained open.

Note:** this PR is not a fix, only reproduces the problem.