dropbox: 81.4.195 -> 83.4.152 (#72021)

Upgrading to latest stable version per
https://www.dropboxforum.com/t5/Desktop-client-builds/bd-p/101003016.
With the previous nixpkgs version dropbox complained that the version is
too old at sign-in.

pkgs/applications/networking/dropbox/default.nix

@@ -7,7 +7,7 @@ assert lib.elem stdenv.hostPlatform.system platforms;
 # Dropbox client to bootstrap installation.
 # The client is self-updating, so the actual version may be newer.
 let
-  version = "81.4.195";
+  version = "83.4.152";
 
   arch = {
     x86_64-linux = "x86_64";