Travis: always timeout

[ZxBing0066]

Current behavior
When run Travis jobs, there is a common error like below:

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received
The build has been terminated

Expected behavior
No timeout error

To Reproduce

1. Just trigger a Travis job
2. Not 100% to see

Minimal demo
No

Package version x.y.z
No

Screenshots

Browser
No

Additional context

[ZxBing0066]

When add the same jobs to CircleCI, it's always break too, and with the out of memory error:

Then I found this issue in jest, it seems like an error when jest run multiple test parallel, there is no enough memory in the VM. For resolve this, I follow this to set max worker number to 2, and then it's resolved!!!

Write this just for record this difficult issue.

Resolve commit id: dfa7f0e