Update Riot to 1.5.12

Summary:
Update Riot to 1.5.12

Changes:

• Upgrade to React SDK 2.2.1
• Revert to Electron 7.1.12 to fix tray icon

Test Plan: Chatted with my friends, sent an image, made a short conference call

Reviewers: Triage Team, JoshStrobl

Reviewed By: Triage Team, JoshStrobl

Subscribers: JoshStrobl

Differential Revision: https://dev.getsol.us/D8428