fix: errors on 404 page

[reuixiy]

After #173, JavaScript is loaded in the head, which makes the 404 page load it also, which caused the following errors on 404 page:

Fixed #199, maybe.

[palant]

Then again, maybe we can avoid loading the script in the 404 page instead? Would be an even better solution.

{{ if ne .Kind "404" }}

It seems that in all other cases head.html is loaded from baseof.html, so the header is guaranteed to be there.