Upgrade Mermaid library to version 8.12.0

To ensure we can use the latest features of Mermaid, upgrades our library to the latest release.

• Before: https://docs.gitlab.com/ee/development/architecture.html#component-diagram
• After: http://eread-upgrade-mermaid-to-8-12-0.178.62.207.141.nip.io/ee/development/architecture.html#component-diagram

CC @aqualls CC @mnichols1