Update log4js.js

Overlooked that there was already a var with '[all]'.

lib/log4js.js

@@ -166,7 +166,7 @@ function configureLevels(levels) {
   if (levels) {
     for (var category in levels) {
       if (levels.hasOwnProperty(category)) {
-        if(category === "all") {
+        if(category === ALL_CATEGORIES) {
           setGlobalLogLevel(levels[category]);
         }
         getLogger(category).setLevel(levels[category]);