Package version updates that follow the well-established and widely-used
commit message format of `attr: 1.0.0 -> 2.0.0` will now be labeled with
the `8.has: package (update)` label. Only ASCII arrows (e.g.  `->`) are
accepted -- Unicode arrows will not trigger the addition of this label.

This is slightly more robust than just checking if `->` exists anywhere
in the title -- now, `attr: move from fetchTarball -> fetchFromGitHub`
won't trigger the addition of the label.

If a commit has an ASCII arrow (`->`) in its title, and the specified
attr will be rebuilt, count it as a package update.