at the moment it's not possible to create version numbers like 2.1-alpha.10 (see http://semver.org/
- they use them too) instead we have to use 2.1-alpha10. But then nuget sorts these version alphabetically which means 2.1-alpha10 is treated as older than 2.1-alpha9. (I was told by @dotnetjunky on twitter that this is not a bug.)
At the moment I have no other choice than to use versions like 2.1.9-alpha and 2.1.10-alpha which are treated in the right order. But this seems to conflict semver.