Merge pull request #381 from blacksails/build-arg-with-equals

Don't cut everything after an equals sign

pkg/dockerfile/buildargs.go

@@ -29,7 +29,7 @@ type BuildArgs struct {
 func NewBuildArgs(args []string) *BuildArgs {
 	argsFromOptions := make(map[string]*string)
 	for _, a := range args {
-		s := strings.Split(a, "=")
+		s := strings.SplitN(a, "=", 2)
 		if len(s) == 1 {
 			argsFromOptions[s[0]] = nil
 		} else {