Address comments:

- Change default value to number.
- Add whitespace in expression.

Author: Arthur Evans

samples/components/computed-property.html

@@ -7,9 +7,9 @@
   </template>
   <script>
     Polymer('square-element', {
-      num: '2',
+      num: 2,
       computed: {
-        square: 'num*num'
+        square: 'num * num'
       }
     });
    </script>