Remove Debian libappindicator dependency

Closes: #1229
Relevant issue:
* https://github.com/electron/electron/issues/27527

The libappindicator package will not be available in the upcoming
Debian "bullseye" release and no appropriate alternative has been
implemented by default in electron / electron-builder.

This is a temporary measure until this issue is dealt with upstream.

_scripts/build.js

@@ -69,6 +69,19 @@ const config = {
     icon: '_icons/icon.svg',
     target: ['deb', 'zip', 'apk', 'rpm', 'AppImage', 'pacman'],
   },
+  deb: {
+    depends: [
+      "libgtk-3-0",
+      "libnotify4",
+      "libnss3",
+      "libxss1",
+      "libxtst6",
+      "xdg-utils",
+      "libatspi2.0-0",
+      "libuuid1",
+      "libsecret-1-0"
+    ]
+  },
   mac: {
     category: 'public.app-category.utilities',
     icon: '_icons/iconMac.icns',