Release 2.1.5

What's Changed

• Update README by @OlenaPostindustria in #907
• Support GMA SDK 10.10.0 by @OlenaPostindustria in #916
• Support GMA SDK 10.11.0 by @OlenaPostindustria in #919
• Implement multiformat ad unit for Original API by @OlenaPostindustria in #914

Full Changelog: 2.1.3...2.1.5