command/fix: use strings instead of Fixer for list

command/fix/command.go

@@ -49,10 +49,18 @@ func (c Command) Run(env packer.Environment, args []string) int {
 	tplF.Close()
 
 	// Run the template through the various fixers
-	fixers := []Fixer{Fixers["iso-md5"]}
+	fixers := []string{
+		"iso-md5",
+	}
+
 	input := templateData
-	for _, fixer := range fixers {
+	for _, name := range fixers {
 		var err error
+		fixer, ok := Fixers[name]
+		if !ok {
+			panic("fixer not found: " + name)
+		}
+
 		input, err = fixer.Fix(input)
 		if err != nil {
 			env.Ui().Error(fmt.Sprintf("Error fixing: %s", err))