www/h2o-devel: update to 2.3.0-beta2

resolves:

• CVE-2019-9512 (Ping Flood)
• CVE-2019-9514 (Reset Flood)
• CVE-2019-9515 (Settings Flood)

PR: 239843
Submitted by: Max Kostikov <max@kostikov.co>
Reported by: Max Kostikov <max@kostikov.co>
Reviewed by: adamw
Approved by: jrm (mentor, implicit)
MFH: 2019Q3
Security: CVE-2019-9512
Security: CVE-2019-9514
Security: CVE-2019-9515
Sponsored by: SkunkWerks, GmbH