Stats Revamp v2: Fix date problem on line chart

[irfano]

Line chart dates were showing as "null" on some devices. I tried to find the reason by using different languages, locales, but every time it was null. It's not showing as null on @ravishanker 's device.

before	after

To test:

1. Go to App Settings (Tap on Avatar at the top right hand corner on My Site -> Find App Settings)
2. Select Debug Settings
3. Find StatsRevampV2FeatureConfig under Features in development enable it and restart app
4. Launch app
5. Go to stats either using quick links or menu
6. Notice a new Views & Visitors card is shown in Insights tab as in the images above (scroll down if necessary)
7. Ensure the dates labels on the line chart are not "null", appearing correctly.

Regression Notes

1. Potential unintended areas of impact
   The date label might be changed incorrectly on other devices which don't show null before.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   I could test only on my device. I'll ask Ravi to test in his environment. His device wasn't shown null before.

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[wpmobilebot]

You can test the WordPress changes on this Pull Request by downloading an installable build (wordpress-installable-build-pr16754-975f451.apk), or scanning this QR code:

[wpmobilebot]

You can test the Jetpack changes on this Pull Request by downloading an installable build (jetpack-installable-build-pr16754-975f451.apk), or scanning this QR code:

[ravishanker]

Thanks for taking caring of this 👍