Fix wrong type of default act_cfg (#7794)

Author: DarthThomas

mmdet/models/backbones/swin.py

@@ -504,7 +504,7 @@ class SwinTransformer(BaseModule):
         use_abs_pos_embed (bool): If True, add absolute position embedding to
             the patch embedding. Defaults: False.
         act_cfg (dict): Config dict for activation layer.
-            Default: dict(type='LN').
+            Default: dict(type='GELU').
         norm_cfg (dict): Config dict for normalization layer at
             output of backone. Defaults: dict(type='LN').
         with_cp (bool, optional): Use checkpoint or not. Using checkpoint