application.js: allow for relative URLs

When running Hugo with relative URLs, as is the case when a developer
runs `hugo` in a regular checkout of this repository, there is no
`https://` prefix, and therefore the current logic failed.

Fix this logic, and while at it, simplify the preceding code a bit.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

assets/js/application.js

@@ -21,10 +21,12 @@ popped = 'state' in window.history;
 initialURL = location.href;
 
 const baseURLPrefix = (() => {
-  const scripts = document.getElementsByTagName('script');
-  const index = scripts.length - 1;
-  const thisScript = scripts[index];
-  return thisScript.src.replace(/^.*:\/\/[^/]*(.*\/)(assets|js)\/[^/]+.js(\?.*)?$/, '$1');
+  const thisScriptSrc =
+    Array.from(document.getElementsByTagName('script'))
+      .pop()
+      .getAttribute('src');
+  return thisScriptSrc
+    .replace(/^(?:[a-z]*:\/\/[^/]*)?(.*\/)(assets|js)\/[^/]+.js(\?.*)?$/, '$1');
 })();
 
 $(document).ready(function() {