Make `zig version` compliant with SemVer (#1113)

The git revision is build metadata and should be appended with a plus sign.

https://semver.org/#spec-item-10
b3a3e2094eJay Weisskopf committed on 6/15/2018, 6:06:56 PM· committed by Andrew Kelleyparentf0697c2
1 file changedLine totals unavailable