Follow redirects, to detect more broken links

When following a incorrect or outdated link to Swift standard library on
developer.apple.com, I get a 301 Moved Permanently first and then a 404
Not Found after following the redirect.  Without following the redirect,
curl exits with "success", causing the link to not be flagged in the
report.

Author: amartini51

bin/preflight

@@ -45,7 +45,7 @@ xpath -q -n -e '//link/@destination' |
 sort -u | cut -f2 -d= | grep -v '^"doc:' | sed 's/^"//; s/"$//' |
 while read url
 do
-    if curl --silent --output /dev/null --fail --head $url
+    if curl --silent --output /dev/null --location --fail --head $url
     then
         echo "     $url"
     else