Retain gh-pages commit history when pushing new version of website (#281)

Summary:
Previously, we force-pushed a newly inited repo - now we actually push the changes.

Pull Request resolved: #281

Test Plan: see D17602805

Reviewed By: Jakepodell

Differential Revision: D17665701

Pulled By: Balandat

fbshipit-source-id: f8eb1474980ac37cb90ccac63dc7bd24e0fc133c

Author: Balandat

scripts/publish_site.sh

@@ -209,12 +209,13 @@ else
   python3 botorch-master/scripts/update_versions_html.py -p "${WORK_DIR}"
   cp -R botorch-master/.circleci new-site/
 
-  # Init as Git repo and push to gh-pages
-  cd new-site || exit
-  git init
+  # move contents of newsite to botorch-gh-pages, preserving commit history
+  rm -rfv ./botorch-gh-pages/*
+  rsync -avh ./new-site/ ./botorch-gh-pages/
+  cd botorch-gh-pages || exit
   git add --all
   git commit -m "Publish version ${VERSION} of site"
-  git push --force "[email protected]:pytorch/botorch.git" master:gh-pages
+  git push
 
 fi