v8.1.0-rc.1

Full Changelog

• Update on Promises
  #1438
• Store and request master cross-signing key
  #1437
• Filter out non-string display names
  #1433
• Bump elliptic from 6.5.2 to 6.5.3
  #1427
• Replace Riot with Element in docs and comments
  #1431
• Remove leftover bits of TSLint
  #1430