truncate at 65535, not 65533

[mikemorris]

The Specials Unicode range actually ends at 0xFFFF or 65535, NOT 65533. The last gapless block should be from 65280 to 65535, the same size as previous blocks.

• https://github.com/mapbox/node-fontnik/blob/master/API.md#getrangestart-number-end-number-arraynumber
• https://github.com/mapbox/node-fontnik/blob/master/bin/build-glyphs#L27-L33
• https://github.com/mapbox/node-fontnik/blob/master/index.js#L27-L30
• https://github.com/mapbox/node-fontnik/blob/master/test/test.js#L134-L153

Refs mapbox/mapbox-gl-native#931