If you want your menu item link to open in a new window, you can do this with the built in WordPress menu item options.
1. Go to Appearance > Menus and click the Screen Options Tab
2. Enable “Link Target”
Under “Show Advanced menu properties”, make sure “Link Target” is checked.
3. Enable new window/tab setting on menu item
On your menu item, expand the settings and check “Open link in a new window/tab”