Change varying name

src/renderers/shaders/ShaderChunk/fog_fragment.glsl

 #ifdef USE_FOG
 
-	float fogDepth = length( fogPosition );
+	float fogDepth = length( vFogPosition );
 
 	#ifdef FOG_EXP2
 

src/renderers/shaders/ShaderChunk/fog_pars_fragment.glsl

 #ifdef USE_FOG
 
 	uniform vec3 fogColor;
-	varying vec3 fogPosition;
+	varying vec3 vFogPosition;
 
 	#ifdef FOG_EXP2
 

src/renderers/shaders/ShaderChunk/fog_pars_vertex.glsl

 #ifdef USE_FOG
 
-  varying vec3 fogPosition;
+	varying vec3 vFogPosition;
 
 #endif

src/renderers/shaders/ShaderChunk/fog_vertex.glsl

-
 #ifdef USE_FOG
-fogPosition = mvPosition.xyz;
-#endif
\ No newline at end of file
+
+	vFogPosition = mvPosition.xyz;
+
+#endif