upgrade webgl_materials_standard to use a combined Roughness-Metallic map.

examples/webgl_materials_standard.html

@@ -126,8 +126,8 @@
 					material.metalness = 1;
 
 					material.map = loader.load( path + 'Cerberus_A.jpg' );
-					material.roughnessMap = loader.load( path + 'Cerberus_R.jpg' );
-					material.metalnessMap = loader.load( path + 'Cerberus_M.jpg' );
+					// roughness is in G channel, metalness is in B channel 
+					material.metalnessMap = material.roughnessMap = loader.load( path + 'Cerberus_RM.jpg' );
 					material.normalMap = loader.load( path + 'Cerberus_N.jpg' );
 
 					material.map.wrapS = THREE.RepeatWrapping;