fix(core feature-detection): Fix loading of modernizr script.

In some situations loading of the modernizr.min.js script failed because
the base url could be incorrect. That is fixed with a non-IE compatible
method of getting the current's script URL, which is safe to use.
The problem surfaced in Plone while loading the Patternslib library and
in between the protect.js script was loaded. The base url was calculated
for the protect.js script and the modernizr script could not be loaded.

Author: thet

src/core/feature-detection.js

@@ -18,15 +18,14 @@
     }
 
     // Get the current script tag's URL.
-    // See: https://stackoverflow.com/a/984656/1337474
-    const scripts = document.getElementsByTagName("script");
-    const script = scripts[scripts.length - 1];
-    let script_url = script.src;
+    const script_url = document.currentScript.src;
     // Get the base URL of the current script tag's URL.
-    script_url = script_url.substring(0, script_url.lastIndexOf("/")) + "/";
+    let base_url = script_url.substring(0, script_url.lastIndexOf("/")) + "/";
+    // The modernizr script is located outside the chunks directory.
+    base_url = base_url.replace("chunks/", "");
 
     // Inject a new one with the modernizr bundle.
     const script_tag = document.createElement("script");
-    script_tag.src = script_url + "modernizr.min.js";
+    script_tag.src = base_url + "modernizr.min.js";
     document.getElementsByTagName("head")[0].appendChild(script_tag);
 })();