add missing file

tests/fixtures/light.tmx

+<?xml version="1.0" encoding="UTF-8"?>
+<map version="1.0" tiledversion="2017.07.26" orientation="orthogonal" renderorder="left-up" width="2" height="2" tilewidth="8" tileheight="8" nextobjectid="1">
+ <tileset firstgid="1" source="terrain.tsx"/>
+ <layer name="Calque de Tile 1" width="2" height="2">
+  <data encoding="csv">
+0,0,
+0,0
+</data>
+ </layer>
+</map>