Also convert cacheto to workaround

plugin/docker.go

@@ -81,7 +81,7 @@ func commandBuild(build Build, dryrun bool) *exec.Cmd {
 	for _, arg := range build.CacheFrom {
 		args = append(args, "--cache-from", arg)
 	}
-	for _, arg := range build.CacheTo.Value() {
+	for _, arg := range build.CacheTo {
 		args = append(args, "--cache-to", arg)
 	}
 	for _, arg := range build.ArgsEnv.Value() {

plugin/impl.go

@@ -65,7 +65,7 @@ type Build struct {
 	Output          string          // Docker build output
 	Pull            bool            // Docker build pull
 	CacheFrom       []string        // Docker build cache-from
-	CacheTo         cli.StringSlice // Docker build cache-to
+	CacheTo         []string        // Docker build cache-to
 	Compress        bool            // Docker build compress
 	Repo            cli.StringSlice // Docker build repository
 	NoCache         bool            // Docker build no-cache