The repository address changed

Previously, the website repository was linked to:

1. GitHub: https://github.com/mpc-hc/website
2. Gemnasium: https://gemnasium.com/mpc-hc/website

respectively. Updated these addresses to reflect the new repository as:

1. GitHub: https://github.com/mpc-hc/mpc-hc.org
2. Gemnasium: https://gemnasium.com/mpc-hc/mpc-hc.org

respectively.