skypeforlinux: 8.34.0.78 -> 8.42.76.54

Semi-automatic update generated by
https://github.com/ryantm/nixpkgs-update tools. This update was made
based on information from
https://repology.org/metapackage/skypeforlinux/versions

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

@@ -6,7 +6,7 @@ let
 
   # Please keep the version x.y.0.z and do not update to x.y.76.z because the
   # source of the latter disappears much faster.
-  version = "8.34.0.78";
+  version = "8.42.76.54";
 
   rpath = stdenv.lib.makeLibraryPath [
     alsaLib
@@ -56,7 +56,7 @@ let
     if stdenv.hostPlatform.system == "x86_64-linux" then
       fetchurl {
         url = "https://repo.skype.com/deb/pool/main/s/skypeforlinux/skypeforlinux_${version}_amd64.deb";
-        sha256 = "1986nvdw1cpj06rq76hjsif0j4z5g2k01v73r4c4n43q7dgzl5z0";
+        sha256 = "1r2wkaa4ss6b8289db3p012nlhvljbx57hp7jc9n0mp19yphd07l";
       }
     else
       throw "Skype for linux is not supported on ${stdenv.hostPlatform.system}";