website: Drop support for Python2. Python3.6+ min version Issue-on: https://gem5.atlassian.net/browse/GEM5-818 Change-Id: I3eff88f1f13168d9069449d1bc6d94105cc2ea5d Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/43805 Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu> Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu> Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>