Fedora version updated in Devstack doc

Docs say that you require Fedora 24/25 to run Devstack, but Devstack
is working in newer versions. Update document to say that Fedora 28
can be used instead.

Closes-Bug: #1797239

Change-Id: Ie5227db9943e5ddb93cd37440165eabbae22f4fc
Signed-off-by: Laura Sofia Enriquez <lsofia.enriquez@gmail.com>
1 file changed