fix demo site links

[edeustace]

the links in the demo site don't work if clicked in the ui, but do work if using the browser url input.

[edeustace]

If a package imports @pie-lib/editable-html, this breaks the nav. I tried importing @pie-lib/icons and it was fine. It's not clear if it's an issue w/ the editable-html package, or with linked packages in a yarn workspace.

[edeustace]

think its related to the math package @pie-lib/math-toolbar

[edeustace]

could be related to this: https://github.com/zeit/next.js/issues/5225