add zoom 12 case

Author: birkskyum

docs/types.md

@@ -187,6 +187,7 @@ type: ["interpolate-projection", ["linear"], ["zoom"],
 
 output at zoom 9.9: "vertical-perspective"
 output at zoom 11: ["vertical-perspective", "mercator", 0.5]
+output at zoom 12: ["vertical-perspective", "mercator", 1]
 output at zoom 12.1: "mercator"
 ```