Fix bad URL in About

<div align="center" >
<img width="374" alt="Screen Shot 2021-04-28 at 3 29 36 pm" src="https://user-images.githubusercontent.com/18750745/116412049-936c9800-a836-11eb-8319-d3d1816cf12d.png">
</div>

If that site is not live, then use the GH Pages URL

https://cooervo.github.io/Algorithms-DataStructures-BigONotation/