docs: fix the "second-instance" event handler signature in the docs (#15548)

docs/api/breaking-changes.md

@@ -35,7 +35,7 @@ app.makeSingleInstance(function (argv, cwd) {
 })
 // Replace with
 app.requestSingleInstanceLock()
-app.on('second-instance', function (argv, cwd) {
+app.on('second-instance', function (event, argv, cwd) {
 
 })
 ```