Update engine to latest playtest.

Author: pchote

mod.config

@@ -9,7 +9,7 @@
 MOD_ID="example"
 
 # The OpenRA engine version to use for this project.
-ENGINE_VERSION="1b0ae1e"
+ENGINE_VERSION="playtest-20170827"
 
 # Enable this to make the default OpenRA mods available for use in your mod.yaml
 # Packages list (via $mod references). Accepts values "True" or "False".