Fix another pre-release version bug (dart-lang/pub_semver#24)

I think at this point we're testing this edge case in all our public
APIs.

Closes dart-lang/pub_semver#17
Closes dart-lang/pub_semver#23
4 files changed
tree: 06903dddff113aaa831f4ed759d30c58761d10a9
  1. pkgs/