add default config name

RedPajama-Data-V2.py

@@ -138,6 +138,8 @@ class RedPajamaDataV2Config(datasets.BuilderConfig):
 class RedPajamaV2(datasets.GeneratorBasedBuilder):
     """ RedPajama V2: Quality annotated Web Text Documents. """
 
+    DEFAULT_CONFIG_NAME = "default"
+
     BUILDER_CONFIGS = [
         RedPajamaDataV2Config(
             name='default',