Loris: [documentation][install centOS] remove reference to bugfix branch

[maltheism]

The bugfix branch no longer exists. There is reference to it in the documentation found here:
https://github.com/aces/Loris/wiki/CentOS-install-guide

[maltheism]

Yay @johnsaigle is fast https://github.com/aces/Loris/pull/5403

[johnsaigle]

My PR doesn't update the CentOS document actually

[johnsaigle]

Actually I think the content of that Wiki page should be deleted and it should link to the CentOS install guide in the repo instead.

[maltheism]

@johnsaigle I updated the link in the wiki from bugfix to master. I think you're right about the wiki page.

[johnsaigle]

I deleted the wiki content and linked to the new install guide: https://github.com/aces/Loris/blob/master/README.CentOS7.md