electron-source: electron 35+ needs gn in PATH

Author: teutat3s

pkgs/development/tools/electron/common.nix

@@ -2,6 +2,7 @@
   lib,
   stdenv,
   chromium,
+  gn,
   nodejs,
   fetchYarnDeps,
   fetchNpmDeps,
@@ -44,6 +45,7 @@ in
   ];
 
   nativeBuildInputs = base.nativeBuildInputs ++ [
+    gn
     nodejs
     yarn
     fixup-yarn-lock