Investigate out-of-memory issue on Node.js 12

[remusao]

The latest Node.js 12 seems but leaking memory when running reverse-index tests. Not sure if it's because of the code or Node.js but this needs to be investigated before it becomes a LTS.

[remusao]

After preliminary investigation it seems like the issue could come from jest itself while performing deepEqual assertions on a big enough instance of FiltersEngine.

[remusao]

The issue seems to be caused by v8:

• Workaround a node >=12.5.0 bug that causes the process not to exit after tests have completed and cancerous memory growth jestjs/jest#8787
• Cancerous memory consumption under specific circumstances nodejs/node#29001