update fluid_cn.rst

doc/fluid/api_cn/fluid_cn.rst

@@ -1060,12 +1060,12 @@ name_scope
 
 .. code-block:: python
           
-	  with name_scope("encoder"):
-             ...
+    with name_scope("encoder"):
+        ...
     with name_scope("decoder"):
-             ...
+        ...
     with name_scope("attention"):
-             ...
+        ...