move lang.Must into logx.Must to make sure output fatal message as json

core/lang/lang.go

@@ -1,16 +1,8 @@
 package lang
 
-import "log"
-
 var Placeholder PlaceholderType
 
 type (
 	GenericType     = interface{}
 	PlaceholderType = struct{}
 )
-
-func Must(err error) {
-	if err != nil {
-		log.Fatal(err)
-	}
-}

core/lang/lang_test.go

@@ -1,7 +0,0 @@
-package lang
-
-import "testing"
-
-func TestMust(t *testing.T) {
-	Must(nil)
-}