Add an extra space to fix the list formatting in the input helper docs

It looks like the list markdown in YUI docs needs to have 2 blank lines at the end to get the correct formatting.

[Current Ember docs site](http://emberjs.com/api/classes/Ember.Handlebars.helpers.html#method_input):
![screen shot 2013-09-13 at 11 52 29 am](https://f.cloud.github.com/assets/54056/1139466/955a0a0a-1c8c-11e3-8dad-563086fdf6f3.png)

Ember docs site with 2 spaces after the checkbox properties list:
![screen shot 2013-09-13 at 11 52 39 am](https://f.cloud.github.com/assets/54056/1139467/96cb24a0-1c8c-11e3-83d1-0126e39b31a2.png)