dropbox: 23.4.18 -> 23.4.19

Dropbox is again updated without a release announcement. I noticed on Friday
that the client was malfunctioning. I was waiting for a release announcement
with the new version number, but as one was not forthcoming, I simply guessed at it.

pkgs/applications/networking/dropbox/default.nix

···
 let
   # NOTE: When updating, please also update in current stable,
   # as older versions stop working
-  version = "23.4.18";
+  version = "23.4.19";
   sha256 =
     {
-      "x86_64-linux" = "0hil9dnhmq4d4yq277w48ql3nw8yfzjqgafb0waw6zbc6a18l7bz";
-      "i686-linux"   = "15hcmqyfyx8z7qx3val5r7b9plckh50iy0mxxh2z1wbh96l03l3a";
+      "x86_64-linux" = "09vjic4yi6g6rbliz4b56swqdpjgw0m7gs2n40xhvbqfd35prafs";
+      "i686-linux"   = "0i2x2s7p1lq315z8198wjlfqr5lqj3mxdcqxz44skrbkmqfd9hab";
     }."${stdenv.system}" or (throw "system ${stdenv.system} not supported");
 
   arch =