Using build metadata in semantic version of a chart causes packager.go to fail

[cbullo]

According to Build Metadata it should be possible to use '+' sign to annotate version with build metadata.
However, the regex packager.go:500 doesn't allow that.

Using this string as a chart version will fail: 0.0.9+63-gf336c00.

[abrisco]

Uh-oh. I'd be happy to review a change to fix this 😀

[cbullo]

Here's the PR:
67
:)

[abrisco]

This is resolved by #82