audit: flip GNU mirror preference.

Now that both the primary and mirror URLs use HTTPS we can flip these
around so the primary URL is the primary URL and we don't have problems
with waiting for mirror propagation.

Library/Homebrew/dev-cmd/audit.rb

@@ -1417,8 +1417,8 @@ class ResourceAuditor
 
   def audit_urls
     # Check GNU urls; doesn't apply to mirrors
-    if url =~ %r{^(?:https?|ftp)://(?!alpha).+/gnu/}
-      problem "Please use \"https://ftpmirror.gnu.org\" instead of #{url}."
+    if url =~ %r{^(?:https?|ftp)://ftpmirror.gnu.org/(.*)}
+      problem "Please use \"https://ftp.gnu.org/gnu/#{$1}\" instead of #{url}."
     end
 
     if mirrors.include?(url)