Allow for proper table creation with Jsonb fields (#1758)

* DataTypeOf should now correctly identify dataValues that are 'json.RawMessage' types as 'jsonb' columns

* move the json check to its own function

* ran gofmt and did some minor tweaks to satisfy CodeClimate

dialect_postgres.go

@@ -1,6 +1,7 @@
 package gorm
 
 import (
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"strings"
@@ -68,9 +69,14 @@ func (s *postgres) DataTypeOf(field *StructField) string {
 		default:
 			if IsByteArrayOrSlice(dataValue) {
 				sqlType = "bytea"
+
 				if isUUID(dataValue) {
 					sqlType = "uuid"
 				}
+
+				if isJSON(dataValue) {
+					sqlType = "jsonb"
+				}
 			}
 		}
 	}
@@ -130,3 +136,8 @@ func isUUID(value reflect.Value) bool {
 	lower := strings.ToLower(typename)
 	return "uuid" == lower || "guid" == lower
 }
+
+func isJSON(value reflect.Value) bool {
+	_, ok := value.Interface().(json.RawMessage)
+	return ok
+}