correct post build doctree removal path (#95)

.github/workflows/publish-docs.yml

@@ -33,7 +33,7 @@ jobs:
           cd docs
           poetry run sphinx-multiversion src build
           # remove any doctrees dirs which aren't needed for publishing
-          find docs/build -type d -name '.doctrees' -exec rm -rf {} +
+          find ./build -type d -name '.doctrees' -exec rm -rf {} +
           cp -r build/* ../pages/
       - name: Add index redirector to latest docs
         run: |