tools: allow [^A-Z] after : in commit message instead of [a-z]
tools: allow [^A-Z] after : in commit message instead of [a-z]

The old regexp choked on the following commit message, which we should
allow according to dvyukov@:
pkg/cover/backend: [symbStart, symbEnd) is a half-closed range

google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller