Update mvt-fixtures to 3.x

[mapsam]

Howdy @BergWerkGIS! Just dropping in to alert you that mvt-fixtures 3.x has been out for some time now and is ready for use. It looks like this library is still on the old version of the suite and is no longer supported. I recommend updating to the 3.x (currently 3.3.0) version and reading through the different FIXTURES highlighted here.

This will also provide some real world fixtures that'll enable you to close out #38

cc @springmeyer

[mapsam]

Oops, seeing that you already have a PR for this over at #34 ... my bad 😄