fix css URL

views/DE/404.pug

@@ -4,7 +4,7 @@ html(lang="de")
     title= "404 - Page not found"
     meta(charset="UTF-8")
     meta(name="viewport", content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no")
-    link(rel="stylesheet", type="text/css", href="https://transfer.hft-stuttgart.de/css/bootstrap/bootstrap.css")
+    link(rel="stylesheet", type="text/css", href="/css/bootstrap.min.css")
     style.
       .container { 
         height: 400px;

views/DE/500.pug

@@ -4,7 +4,7 @@ html(lang="de")
     title= "500 - Internal Server Error"
     meta(charset="UTF-8")
     meta(name="viewport", content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no")
-    link(rel="stylesheet", type="text/css", href="https://transfer.hft-stuttgart.de/css/bootstrap/bootstrap.css")
+    link(rel="stylesheet", type="text/css", href="/css/bootstrap.min.css")
     style.
       .container { 
         height: 400px;