fixing typo.

underscore.js

@@ -385,7 +385,7 @@
     return (n != null) && !guard ? slice.call(array, 0, n) : array[0];
   };
 
-  // Returns everything but the last entry of the array. Especcialy useful on
+  // Returns everything but the last entry of the array. Especially useful on
   // the arguments object. Passing **n** will return all the values in
   // the array, excluding the last N. The **guard** check allows it to work with
   // `_.map`.