valid tile template do not need jpg/png

[mikelmaron]

mapbox tile endpoints do not have file suffixes, so adding mapbox tile source fails. tile templates do not require the file suffix be specified.

[thadk]

I took away these checks on my Docker instance of Field Papers. A Mapbox Studio styles API tiles-based map now displays correctly in the browser--even after atlas creation. For the PDF, though, all the tiles are still coming out completely black with this API, presumably indicating some sort of error like fieldpapers/fieldpapers#139 .

Here is an example User-defined URL (I use #png at the end of the URL to skip the client and server side regex's but effect is same once you apply this patch and remove it) using Mapbox Studio styles which is totally black in PDF:
http://fieldpapers.org/atlases/2d1dtjgf
Creation URL:
http://fieldpapers.org/compose?lat=6.28271&lon=-10.75551&provider=https%3A%2F%2Fapi.mapbox.com%2Fstyles%2Fv1%2Fthadk%2Fcj48xoecv25mj2rogw8ejoguo%2Ftiles%2F256%2F%7Bz%7D%2F%7Bx%7D%2F%7By%7D%3Faccess_token%3Dpk.eyJ1IjoidGhhZGsiLCJhIjoidWlIX1J4OCJ9.BZnfrT_Jdc8aSQyWV8fL7g%23png&title=cannedthad&zoom=17#15/6.2914/-10.7451
via: http://fieldpapers.org/make-canned-atlas-template

[thadk]

i created a proxy to workaround this issue for Mapbox Studio. The source code and instructions are at https://github.com/thadk/fieldpapers-mapboxstudio-proxy
and the atlas provider proxy server is at https://fieldpapers-mapboxstudio-proxy.herokuapp.com/