Set suppress_errors=false in Franklin build (#610)

We broke the JuliaCon website on the first day because an error was suppressed.  The error had been live for a while, but a change to surrounding code caused it to move from minor annoyance to catastrophic.  This moves us to a stricter mode where such errors are not allowed at all.

.github/workflows/Deploy.yml

@@ -49,7 +49,7 @@ jobs:
         Pkg.instantiate()
 
         using Franklin
-        optimize(minify=false, prerender=false)
+        optimize(minify=false, prerender=false, suppress_errors=false)
     - name: Deploy (preview)
       if: github.event_name == 'pull_request' && ! github.event.pull_request.head.repo.fork # if this build is a PR build and the PR is NOT from a fork
       uses: JamesIves/github-pages-deploy-action@releases/v4