Fix type for tray options' menuItems property

[jouni-kantola]

Fix #78

[jouni-kantola]

After trying this out for a bit, maybe the properties shouldn't be exported as optional. I suggest changing the interface TrayOptions to:

export interface TrayOptions {
    icon: string;
    menuItems: TrayMenuItem[];
}

The reasoning for this:

• If icon is omitted, you end up with a tray slot with an empty icon in Windows 11 and MacOS.
• If menuItems are omitted, the application crashes in Windows 11 and MacOS.

The above also matches the docs ("Optional" isn't mentioned).