Semver ranges: use "semver" package

[ronkorving]

If you were to use the semver package, you could easily have full semver range syntax support.

[typicode]

Thank you for the suggestion, v3.0.2 now uses https://github.com/substack/semver-compare :)

[a-x-]

Why your description is not say it?

[a-x-]

from readme.md:

Important: >= is the only operator supported by please-upgrade-node (e.g. >=6, >=6.0, >=6.0.0).