docset: use --icon-2x instead of manual copy

Author: hynek

tox.ini

@@ -131,6 +131,5 @@ allowlist_externals =
 commands =
     rm -rf attrs.docset attrs.tgz docs/_build
     sphinx-build -n -T -W -b html -d {envtmpdir}/doctrees docs docs/_build/html
-    doc2dash --index-page index.html --icon docs/_static/docset-icon.png --online-redirect-url https://www.attrs.org/en/latest/ docs/_build/html
-    cp docs/_static/docset-icon@2x.png attrs.docset/icon@2x.png
+    doc2dash --index-page index.html --icon docs/_static/docset-icon.png --icon-2x docs/_static/docset-icon@2x.png  --online-redirect-url https://www.attrs.org/en/latest/ docs/_build/html
     tar --exclude='.DS_Store' -cvzf attrs.tgz attrs.docset