Downgrade PREVIEW version

Latest "subpath" support is broken.

Opening anything but the root path gives a blank page.
In the console a "Failed to load module script" error is shown.
This is caused because any path after the root is considered to be part of the root. Thus, invalid urls are used for all requests.

Example:
  Root: "localhost:4567/manga"
  
  Open page on "localhsot:4567/manga/44" will lead to this url being used as the root.

versionToServerVersionMapping.json

@@ -1,6 +1,7 @@
 [
   {
-    "uiVersion": "PREVIEW",
+    "tag": "PREVIEW",
+    "uiVersion": "r2817",
     "serverVersion": "r1910"
   },
   {