Add Error Handler for "x is out of range"

[millzpaugh]

[error] required parameter x is out of range of possible values based on z value has recently surfaced while looking through upload errors. It's very similar to required parameter y is out of range, which is currently handled here https://github.com/mapbox/mapbox-tile-copy/blob/master/lib/tilelivecopy.js#L29

Let's add the x is out of range error to this conditional so both x & y out of range are handled in the same conditional statement on L29.

cc @mapsam

[springmeyer]

This looks like it landed in https://github.com/mapbox/mapbox-tile-copy/commit/706c7a43cc5310e3efe4bb0d30b601068b475fce