reformat & add default_marker to 1x for Emerald

[incanus]

Fixed the missing reference to default_marker in 1x; reformatted.

/cc @peterqliu

[incanus]

@peterqliu There are other problems in your 1x sheet:

"us_highway_1": {
  "height": 24,
  "pixelRatio": 1,
  "sdf": false,
  "width": 24.5,
  "x": 0,
  "y": 82
},

Namely that we can't have non-integer pixel values like the width here. I'm not sure what we normally do for halves like this, but this crashes the app hard as we assume integer values.

Aside from the fix, we need to test sprites on both 1x and 2x devices, as they are entirely different sprites. You can do this by testing on an iPad 2 simulator; that's the only one left these days that is supported by iOS 7 but that isn't retina.

[peterqliu]

taken care of in #45