Account for 4 influnces per vertex in vertex shader

src/renderers/shaders/ShaderLib.js

@@ -1104,6 +1104,8 @@ THREE.ShaderLib = {
 
 			"			vec4 skinned  = boneMatX * skinVertex * skinWeight.x;",
 			"			skinned 	  += boneMatY * skinVertex * skinWeight.y;",
+			"			skinned 	  += boneMatZ * skinVertex * skinWeight.z;",
+			"			skinned 	  += boneMatW * skinVertex * skinWeight.w;",
 
 			"			displacedPosition  = skinned.xyz;",