element-desktop: fix missing app icon

Element Desktop switched to generation of icons
with electron-builder, and no longer generates the
icons with different resolutions. This commit simply
copies the app icon into the outpath.

pkgs/by-name/el/element-desktop/package.nix

@@ -7,7 +7,7 @@
   yarn,
   nodejs,
   jq,
-  electron_37,
+  electron_38,
   element-web,
   sqlcipher,
   callPackage,
@@ -22,7 +22,7 @@ let
   pinData = import ./element-desktop-pin.nix;
   inherit (pinData.hashes) desktopSrcHash desktopYarnHash;
   executableName = "element-desktop";
-  electron = electron_37;
+  electron = electron_38;
   keytar = callPackage ./keytar {
     inherit electron;
   };
@@ -111,11 +111,9 @@ stdenv.mkDerivation (
       cp $out/share/element/electron/lib/i18n/strings/en_EN.json $out/share/element/electron/lib/i18n/strings/en-us.json
       ln -s $out/share/element/electron/lib/i18n/strings/en{-us,}.json
 
-      # icons
-      for icon in $out/share/element/electron/build/icons/*.png; do
-        mkdir -p "$out/share/icons/hicolor/$(basename $icon .png)/apps"
-        ln -s "$icon" "$out/share/icons/hicolor/$(basename $icon .png)/apps/element.png"
-      done
+      # icon
+      mkdir -p "$out/share/icons/hicolor/icon/apps"
+      ln -s "$out/share/element/electron/build/icon.png" "$out/share/icons/hicolor/icon/apps/element.png"
 
       # desktop item
       mkdir -p "$out/share"