failure if x.y.0 version is not released

[mathause]

If a package does not release a x.y.0 version we fail in this line:

minimum-dependency-versions/minimum_versions.py

Line 175 in 2aa8d51

return releases[spec.name][version]

we should allow this by using the first version >= x.y.0. One package is netCDF 1.7 conda-forge/netcdf4-feedstock#164 (or regionmask 0.12)

I am happy to take a look but could be good to fix #17 first.