fix: User innerWidth instead of outerWidth

When falling back for no native matchMedia support, window width was set using `window.outerWidth`. This is the incorrect property to use, as `outerWidth` includes window borders.

`window.innerWidth` only includes the scrollbar, which behaves the same way as a `min-width` media query. This is what we want to use.

Note that this was mostly affecting IE9. Less than IE9 doesn't support media queries, and greater than IE9 was never falling back to this condition, as it natively supports matchMedia.