Fix favicon aspect ratio issue

[krisstern]

Reproduction steps

Go to the tab of stats.jenkins.io to observe the aspect ratio compared to that of https://www.jenkins.io/

Expected Results

Favicon to look like the one in https://www.jenkins.io/

Actual Results

Now our favicon looks kind of fat with a different favicon image

Anything else?

No response

[720Florian]

I work on this issue

[krisstern]

Completed via #189