pin mkdocs_autorefs to compatible version

fixes an error in mkdocs_autorefs/plugin.py, line 77:

TypeError: type 'BasePlugin' is not subscriptable

Author: ischneider

setup.py

@@ -41,7 +41,8 @@
     'mkdocs==1.3',
     'mkdocs-click==0.7.0',
     'mkdocs-material==8.2.11',
-    'mkdocstrings==0.18.1'
+    'mkdocstrings==0.18.1',
+    'mkdocs_autorefs==1.0.1',
 ]
 
 setup(