Update fedora.md

Docker-DCO-1.1-Signed-off-by: Alexander Shopov <ash@kambanaria.org> (github: alshopov)

Squashed by

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)

replaces #6478
If you are behind a HTTP proxy server