The devtools console gives it away:
Mixed Content: The page at ‘https://rowansdabomb.github.io/‘ was loaded over HTTPS, but requested an insecure script ‘http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.12.2.min.js‘. This request has been blocked; the content must be served over HTTPS.
Your page is being served via HTTPS (which is great) but it tries to load jQuery via HTTP, which is not encrypted traffic and a potential security issue, which is why the browser refuses to load it.
Change the script source to HTTPS and you’re good to go.
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solved No javascript source from Github pages [closed]