5.1.0 shipped the stricter REGEXP flag handling (unsupported flags, including
g/y, threw). 5.1.1 ships the refinement that landed just after: lastIndex is
reset per row so g is a no-op and y (sticky) anchors at the start, while
genuinely invalid flags still throw. The behavior change rode in via the earlier
feat commit; this bumps the version so it can be published (5.1.0 is taken).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>