Really "Dual license" GPL/MIT in package/lib/vow.js ?

Hello, 

I would like to use the component in a project. Now I have seen that in "package/lib/vow.js" a "dual licensing" is specified. However, it says "gpl AND mit" and not "gpl OR mit". Does this mean that you can now choose one of the licenses or does it mean that you have to follow both licenses? 

Thanks for your help