electron - explicitly disable spellchecker

It will be enabled by default starting with Electron 9

test/unit/electron/index.js

@@ -116,6 +116,7 @@ app.on('ready', () => {
 			nodeIntegration: true,
 			enableWebSQL: false,
 			enableRemoteModule: false,
+			spellcheck: false,
 			nativeWindowOpen: true,
 			webviewTag: true
 		}