Use container width instead of window width for lazy-load

[rmunch]

When you use the container option when using a scrolling container, images are tested against the window width to determine whether they are in the viewport instead of against the container's dimensions.

In my case, I have a scrolling container that only fills up 2/3 of the screen, so there are a few images that aren't visible that still get lazy-loaded. Ideally they would only load as you scroll the container.

Thanks for this well-done lazy-loader!

[dinbror]

Fixed in 1.8.0

[dinbror]

Better late than never ;)