relative link changed to https

Noticed that one of the links on the opening pages was a relative path not an https path. Got a 404 error when trying to view it via my local IPython notebook.

"[camdavidsonpilon.github.io/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/](camdavidsonpilon.github.io/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/)"

Changed to:

"[<b>https://</b>camdavidsonpilon.github.io/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/](https://camdavidsonpilon.github.io/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/)"