Fix bind polyfill typo : funcArgs -> fnArgs

Author: lakbychance

challenges/functions-challenges.md

@@ -114,7 +114,7 @@ if(!Function.prototype.bind){
         var fnArgs = Array.prototype.slice.call(arguments, 1);
 
         return function(){
-            var allArgs = funcArgs.concat(Array.prototype.slice.call(arguments))
+            var allArgs = fnArgs.concat(Array.prototype.slice.call(arguments))
             fn.apply(context, allArgs);
         };
     }
@@ -641,4 +641,4 @@ This is a well known JavaScript pattern called as __Publish/Subscribe Pattern__
 
 <br />
 
-[[↑] Back to top](#home)
+[[↑] Back to top](#home)