publish-gh-pages: include gitignore

publish-gh-pages

@@ -4,9 +4,13 @@ set -eu
 git push
 ./build-doc --github-pages
 git checkout gh-pages
-git checkout master -- '*.png' _config.yml
+git checkout master -- \
+  .gitignore \
+  '*.png' \
+  _config.yml \
+;
 cp out/README.html index.html
 git add index.html
 git commit --message "$(git log -n1 --pretty='%H' master)"
-git push --force
+git push
 git checkout -