Force relative path for config/config.js

Closes #118, again.

index.html

@@ -12,7 +12,7 @@
       <strong>We're sorry but OwnTracks doesn't work properly without JavaScript enabled. Please enable it to continue.</strong>
     </noscript>
     <div id="app"></div>
-    <script src="/config/config.js"></script>
+    <script src="./config/config.js"></script>
     <script type="module" src="/src/main.js"></script>
   </body>
 </html>