v0.7.4-rc.1

Full Changelog

• Remove babel-polyfill
  #321
• Update build process for ES6
  #320
• 'babel' is not a babel package anymore
  #319
• Add Babel for ES6 support
  #318
• Move screen sharing check/error
  #317
• release.sh: Bail early if there are uncommitted changes
  #316