Fix gorm.Open dialect

Fix gorm.Open dialect from 'sqlite' to 'sqlite3'

documents/README.md

@@ -48,7 +48,7 @@ type Product struct {
 }
 
 func main() {
-  db, err := gorm.Open("sqlite", "test.db")
+  db, err := gorm.Open("sqlite3", "test.db")
   if err != nil {
     panic("failed to connect database")
   }