[FIX] double slashes in avatar url

[shiqimei]

Proposed changes

https://app.asana.com/0/633285093795758/1177305720214377/f

Issue(s)

N/A

How to test or reproduce

• Install any of apps here (private repo)
• Turn on Game Center experimental feature in the Admin -> General -> Apps
• Open the game in the game center
• Check Admin -> View Logs or logs from terminal to see if avatarUrl's value correct

Screenshots

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Hotfix (a major bugfix that has to be merged asap)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Changelog

Further comments

[ggazzo]

;)