Upgrade yaml to v3

As requested in "Update the yaml dependency to v3? #206".

README.md

@@ -170,7 +170,7 @@ func main() {
 
 Note: if test are failing due missing package, please execute:
 
-    go get gopkg.in/yaml.v2
+    go get gopkg.in/yaml.v3
 
 ### Transformers
 

go.mod

@@ -2,4 +2,4 @@ module github.com/imdario/mergo
 
 go 1.13
 
-require gopkg.in/yaml.v2 v2.3.0
+require gopkg.in/yaml.v3 v3.0.0

go.sum

@@ -1,4 +1,4 @@
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v2 v2.3.0 h1:clyUAQHOM3G0M3f5vQj7LuJrETvjVot3Z5el9nffUtU=
-gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0 h1:hjy8E9ON/egN1tAYqKb61G10WtihqetD4sz2H+8nIeA=
+gopkg.in/yaml.v3 v3.0.0/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

mergo_test.go

@@ -13,7 +13,7 @@ import (
 	"time"
 
 	"github.com/imdario/mergo"
-	"gopkg.in/yaml.v2"
+	"gopkg.in/yaml.v3"
 )
 
 type simpleTest struct {
@@ -603,18 +603,18 @@ func TestMapsWithNilPointer(t *testing.T) {
 func TestYAMLMaps(t *testing.T) {
 	thing := loadYAML("testdata/thing.yml")
 	license := loadYAML("testdata/license.yml")
-	ft := thing["fields"].(map[interface{}]interface{})
-	fl := license["fields"].(map[interface{}]interface{})
+	ft := thing["fields"].(map[string]interface{})
+	fl := license["fields"].(map[string]interface{})
 	// license has one extra field (site) and another already existing in thing (author) that Mergo won't override.
 	expectedLength := len(ft) + len(fl) - 1
 	if err := mergo.Merge(&license, thing); err != nil {
 		t.Error(err.Error())
 	}
-	currentLength := len(license["fields"].(map[interface{}]interface{}))
+	currentLength := len(license["fields"].(map[string]interface{}))
 	if currentLength != expectedLength {
 		t.Errorf(`thing not merged in license properly, license must have %d elements instead of %d`, expectedLength, currentLength)
 	}
-	fields := license["fields"].(map[interface{}]interface{})
+	fields := license["fields"].(map[string]interface{})
 	if _, ok := fields["id"]; !ok {
 		t.Errorf(`thing not merged in license properly, license must have a new id field from thing`)
 	}