Docker build fails due to upstream dep issue

[Dan Chaffelson]

Logs like:

#5 18.53 # github.com/golang/dep/gps
#5 18.53 pkg/mod/github.com/golang/dep@v0.5.4/gps/constraint.go:103:21: cannot use sv (type *semver.Version) as type semver.Version in field value
#5 18.53 pkg/mod/github.com/golang/dep@v0.5.4/gps/constraint.go:122:16: invalid type assertion: c.(semver.Version) (non-interface type *semver.Constraints on left)
#5 18.53 pkg/mod/github.com/golang/dep@v0.5.4/gps/constraint.go:149:4: undefined: semver.Constraint

Relates to issue: golang/dep#2223
Can be fixed by using this suggestion on that issue: golang/dep#2223 (comment)

[Will Norris]

Fixed in #82