discord: 0.0.18 -> 0.0.19

As of this commit date, v0.0.18 won't let you start up - the auto-check
for available updates aborts application startup.

pkgs/applications/networking/instant-messengers/discord/default.nix

@@ -1,7 +1,7 @@
 { branch ? "stable", callPackage, fetchurl, lib, stdenv }:
 let
   versions = if stdenv.isLinux then {
-    stable = "0.0.18";
+    stable = "0.0.19";
     ptb = "0.0.29";
     canary = "0.0.136";
   } else {
@@ -14,7 +14,7 @@ let
     x86_64-linux = {
       stable = fetchurl {
         url = "https://dl.discordapp.net/apps/linux/${version}/discord-${version}.tar.gz";
-        sha256 = "1hl01rf3l6kblx5v7rwnwms30iz8zw6dwlkjsx2f1iipljgkh5q4";
+        sha256 = "GfSyddbGF8WA6JmHo4tUM27cyHV5kRAyrEiZe1jbA5A=";
       };
       ptb = fetchurl {
         url = "https://dl-ptb.discordapp.net/apps/linux/${version}/discord-ptb-${version}.tar.gz";