Fix broken images in Cloudflare preview builds (#1244)

Moved from #1232 

This change updates production.sh to call hugo
differently in Cloudflare environments than otherwise.
- In Cloudflare, the variable $CF_PAGES_URL tracks the
  base URL of a PR build or the production deploy and needs
  to be part of the hugo command.
- Locally, this variable is not set so don't try to use it.

To help with debugging, log the environment we are building in.

## Tests
- [x] Local build works, image shows up correctly
- [x] PR build works, image shows up correctly

Author: mdlinville

scripts/production.sh

@@ -3,7 +3,13 @@
 # Build the English docs from this branch
 hugo mod get -u
 rm -rf public
-hugo
+if [ -n "$CF_PAGES_URL" ]; then
+    echo "Building in Cloudflare"
+    hugo -b $CF_PAGES_URL
+else
+    echo "Building locally"
+    hugo
+fi
 rm public/sitemap.xml
 mv public/en/sitemap.xml public/sitemap.xml
 rm -rf public/ja