Update vendors.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/blang/semver/json.go

@@ -0,0 +1,23 @@
+package semver
+
+import (
+	"encoding/json"
+)
+
+// MarshalJSON implements the encoding/json.Marshaler interface.
+func (v Version) MarshalJSON() ([]byte, error) {
+	return json.Marshal(v.String())
+}
+
+// UnmarshalJSON implements the encoding/json.Unmarshaler interface.
+func (v *Version) UnmarshalJSON(data []byte) (err error) {
+	var versionString string
+
+	if err = json.Unmarshal(data, &versionString); err != nil {
+		return
+	}
+
+	*v, err = Parse(versionString)
+
+	return
+}