Update Electron to v29

This brings lots of small fixes & improvements, particularly by just
bringing a newer Chromium, but also means dropping support for both Mac
OS < 10.15 (pre-Catalina) and Windows < 10 (i.e. dropping 8 & 8.1, as
Windows 7 has been unsupported in the server for some time anyway).

Author: pimterry

package-lock.json

@@ -145,7 +145,7 @@
     "babel-plugin-transform-async-to-generator": "^6.24.1",
     "babel-preset-env": "^1.7.0",
     "cross-env": "^7.0.3",
-    "electron": "^22.3.26",
+    "electron": "^29.1.5",
     "electron-builder": "^24.13.3",
     "lodash": "^4.17.21",
     "node-fetch": "^2.6.7",