Replace json with ujson

[TaiJuWu]

All Submissions:

• [X] Have you followed the guidelines stated in CONTRIBUTING.md file?
• [X] Have you checked to ensure there aren't any other open Pull Requests for the desired changed?

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [X] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

New Feature Submission:

• [X] Does your submission pass the tests?
• [X] Have you linted your code locally prior to submission?

Changes To Core Features:

• [X] Have you added an explanation of what your changes do and why you'd like us to include them?
• [X] Have you written new tests for your core changes, as applicable?
• [X] Have you successfully ran tests with your changes locally?

After these steps, you're ready to open a pull request.

a. Give a descriptive title to your PR.

Replace json with ujson. The reason is ujson is faster than json.

reference: https://medium.com/dataweave/json-vs-simplejson-vs-ujson-2887b2c128b2

b. Describe your changes.

Replace json with ujson. c. Put closes #XXXX in your comment to auto-close the issue that your PR fixes (if such).

[TaiJuWu]

I didn't find any reason made integration test fail...

[Alek99]

Hi just tested and this does seem to work when running in prod mode when I try it