Handle pre-release semantics by adjusting the max version of ranges (dart-lang/pub_semver#28)

Rather than adding special-cases to each operation, we now just modify
the upper bound of version ranges when the special pre-release
semantics would come into play.

Closes dart-lang/pubdart-lang/pub_semver#1885
11 files changed
tree: 3cebedc238b899db008fafbdfa03e11394e5ab72
  1. pkgs/