fix wiki link on home page

[Jas Phua]

Hi there,

Could someone please fix the wiki URL on the Crisis Commons home page/
right nav please?

It's currently pointing to the following which results in a 404 error:
http://crisiscommons.org/wiki/index.php?title=Main_Page

and should probably be going to:
http://wiki.crisiscommons.org/

Thanks,
-Jas