Fix favicon image
Fix favicon image

Convert the favicon.ico to .ico format. It actually was a .png file with
a misleading extension.

tddv/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org,pombredanne/readthedocs.org,tddv/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org,pombredanne/readthedocs.org,rtfd/readthedocs.org,pombredanne/readthedocs.org,rtfd/readthedocs.org,tddv/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org