size enhancement as ternary and _.size(arr) test case

test/collections.js

@@ -275,6 +275,7 @@ $(document).ready(function() {
 
   test('collections: size', function() {
     equal(_.size({one : 1, two : 2, three : 3}), 3, 'can compute the size of an object');
+    equal(_.size([1, 2, 3]), 3, 'can compute the size of an array');
   });
 
 });

underscore.js

@@ -309,11 +309,7 @@
 
   // Return the number of elements in an object.
   _.size = function(obj) {
-    if (_.isArray(obj)) {
-      return obj.length;
-    }else{
-      return _.keys(obj).length;
-    }
+    return _.isArray(obj) ? obj.length : _.keys(obj).length;
   };
 
   // Array Functions