remove redundant variable of for loop

mapstructure.go

diff --git a/mapstructure.go b/mapstructure.go
index a554e79..d1cb607 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -698,7 +698,7 @@
 		if !rawMapVal.IsValid() {
 			// Do a slower search by iterating over each key and
 			// doing case-insensitive search.
-			for dataValKey, _ := range dataValKeys {
+			for dataValKey := range dataValKeys {
 				mK, ok := dataValKey.Interface().(string)
 				if !ok {
 					// Not a string key
@@ -746,7 +746,7 @@
 
 	if d.config.ErrorUnused && len(dataValKeysUnused) > 0 {
 		keys := make([]string, 0, len(dataValKeysUnused))
-		for rawKey, _ := range dataValKeysUnused {
+		for rawKey := range dataValKeysUnused {
 			keys = append(keys, rawKey.(string))
 		}
 		sort.Strings(keys)
@@ -761,7 +761,7 @@
 
 	// Add the unused keys to the list of unused keys if we're tracking metadata
 	if d.config.Metadata != nil {
-		for rawKey, _ := range dataValKeysUnused {
+		for rawKey := range dataValKeysUnused {
 			key := rawKey.(string)
 			if name != "" {
 				key = fmt.Sprintf("%s.%s", name, key)

mapstructure_test.go

diff --git a/mapstructure_test.go b/mapstructure_test.go
index ea21924..cc1fffb 100644
--- a/mapstructure_test.go
+++ b/mapstructure_test.go
@@ -856,10 +856,10 @@
 	t.Parallel()
 
 	input := []map[string]interface{}{
-		map[string]interface{}{
+		{
 			"foo": "bar",
 		},
-		map[string]interface{}{
+		{
 			"bar": "baz",
 		},
 	}