shells/iris: Update to 0.4.21

Changelog:

• https://github.com/versenilvis/IRIS/releases/tag/v0.4.12
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.13
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.14
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.15
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.18
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.19
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.20
• https://github.com/versenilvis/IRIS/releases/tag/v0.4.21

Reported by: GitHub (watch releases)