Update index.html

change image (orginal) https://cloud.githubusercontent.com/assets/5073946/3721468/c9ad7aa2-1660-11e4-85ec-931c15cbd959.png to image (small) https://cloud.githubusercontent.com/assets/5073946/3721751/7d4b2a12-1663-11e4-9b1e-2dcfd32a6968.png