Would you consider creating a 3.12 release? According to their website this is a LTS release:
HHVM releases a point (stable) release on the order of every 8 weeks. Every third major point release of HHVM (e.g, 3.6, 3.9) is considered a long-term support (LTS) release. These releases are supported for nearly one year (48 weeks), and are backported with critical bug fixes and security patches. At any given time, there will be two supported LTS releases.
Would you consider creating a 3.12 release? According to their website this is a LTS release: