Update PBRTerrain.j3md

jme3-terrain/src/main/resources/Common/MatDefs/Terrain/PBRTerrain.j3md

@@ -274,6 +274,8 @@ MaterialDef PBR Terrain {
             STATIC_SUN_EXPOSURE : StaticSunExposure
             BRIGHTEN_INDOOR_SHADOWS : BrightenIndoorShadows
 
+            USE_FIRST_LAYER_AS_TRANSPARENCY : UseFirstLayerAsTransparency
+
             DISCARD_ALPHA : AlphaDiscardThreshold
 
             USE_FOG : UseFog