WIP Adjust box version validation to packer implementation and vagrant documentation

[TuningYourCode]

Adjusts the box version validation to conform with packer implementation and vagrant documentation.

Fixes #14

[dlundgren]

I just took a look at the packer implementation, and it doesn't implement a version check, instead relying on vagrant-cloud to handle the versioning. I also tested several of the versions that were moved from good to bad against vagrant-cloud and they are working to allow uploads.

I think in this instance I'd rather keep the feature parity and allow the various permutations of x, x.y and x.y.z.

I did notice that vagrant-cloud will reject a version specified as v2018.06.09 though.

[dlundgren]

#19 replaces this to keep the versions less strict