enable "clean" on pkgdown action (#55)

enable "clean" on pkgdown action to see if it will clear out old
vignettes/articles that should no longer exist

.github/workflows/pkgdown.yaml

@@ -45,6 +45,6 @@ jobs:
         if: github.event_name != 'pull_request'
         uses: JamesIves/[email protected]
         with:
-          clean: false
+          clean: true
           branch: gh-pages
           folder: docs