Updated DEPS for sync js lib

[AlexeyBarabash]

Fixes brave/brave-browser#3515 .
New sync lib head commit for DEPS is brave/sync@76bf8f1 .

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone

Test Plan:

The STR from brave/brave-browser#3515

1. Create sync chain on brave-core device A
2. Connect to the sync chain device B with code words
3. On the device A open the following tabs:
   brave://bookmarks/
   https://www.bing.com/search?q=BCA-01&qs=n&form=QBLH&sp=-1&pq=bca-01&sc=8-6&sk=&cvid=4CE2DC7674794F3C89E4F55DE31BBD2A
   https://www.bing.com/search?q=BCA-02&qs=n&form=QBRE&sp=-1&pq=bca-02&sc=8-6&sk=&cvid=DA80C45365A54CF4880E4F853CE72332
   https://www.bing.com/search?q=BCA-03&qs=n&form=QBRE&sp=-1&pq=bca-03&sc=8-6&sk=&cvid=5E00C210D471463EB9ECF64D9EC703DA
4. On device A bookmark tabs of BCA-01 and BCA-02 as quick as possible
5. On device B wait until BCA-01 and BCA-02 appear. When this happened as quick as possible, on device A unbookmark BCA-02 tab and bookmark BCA-03 tab
6. On device B BCA-02 is removed

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source