update vendor

vendor/gopkg.in/yaml.v2/decode.go

@@ -251,7 +251,7 @@ func (d *decoder) callUnmarshaler(n *node, u Unmarshaler) (good bool) {
 //
 // If n holds a null value, prepare returns before doing anything.
 func (d *decoder) prepare(n *node, out reflect.Value) (newout reflect.Value, unmarshaled, good bool) {
-	if n.tag == yaml_NULL_TAG || n.kind == scalarNode && n.tag == "" && (n.value == "null" || n.value == "" && n.implicit) {
+	if n.tag == yaml_NULL_TAG || n.kind == scalarNode && n.tag == "" && (n.value == "null" || n.value == "~" || n.value == "" && n.implicit) {
 		return out, false, false
 	}
 	again := true

vendor/gopkg.in/yaml.v2/decode_test.go

@@ -438,6 +438,9 @@ var unmarshalTests = []struct {
 	{
 		"foo: ''",
 		map[string]*string{"foo": new(string)},
+	}, {
+		"foo: null",
+		map[string]*string{"foo": nil},
 	}, {
 		"foo: null",
 		map[string]string{"foo": ""},
@@ -446,6 +449,18 @@ var unmarshalTests = []struct {
 		map[string]interface{}{"foo": nil},
 	},
 
+	// Support for ~
+	{
+		"foo: ~",
+		map[string]*string{"foo": nil},
+	}, {
+		"foo: ~",
+		map[string]string{"foo": ""},
+	}, {
+		"foo: ~",
+		map[string]interface{}{"foo": nil},
+	},
+
 	// Ignored field
 	{
 		"a: 1\nb: 2\n",

vendor/gopkg.in/yaml.v2/yaml.go

@@ -140,7 +140,7 @@ func unmarshal(in []byte, out interface{}, strict bool) (err error) {
 // For example:
 //
 //     type T struct {
-//         F int "a,omitempty"
+//         F int `yaml:"a,omitempty"`
 //         B int
 //     }
 //     yaml.Marshal(&T{B: 2}) // Returns "b: 2\n"