relax required attrs version

tomjnixon · tomjnixon · commit cf41183c7129 · 2022-01-26T18:20:48.000Z
diff --git a/setup.py b/setup.py
@@ -17,7 +17,7 @@
     install_requires=[
         'numpy~=1.14',
         'scipy~=1.0',
-        'attrs~=19.3',
+        'attrs>=19.3,<22',
         'ruamel.yaml~=0.15',
         'lxml~=4.4',
         'six~=1.11',
