Bump to 3.6.2-carto.4, using mapnik v3.0.15.6 [publish binary]

Author: Rafa de la Torre

CHANGELOG.carto.md

@@ -2,7 +2,7 @@
 
 ## 3.6.2-carto.4
 
-**Release date**: 2018-mm-dd
+**Release date**: 2018-03-14
 
 Changes:
  - Update mapnik to [v3.0.15.6](https://github.com/CartoDB/mapnik/blob/v3.0.15-carto/CHANGELOG.carto.md#30156), which includes fixes and improvements for raster markers cache.