Made regexp extracting GFS directy names more robust.

Issue 1409: It seems the directory listing HTML changed, and this
caused the regexp extracting the GFS directory names to capture
HTML elements, thus making the names always invalid.

Resolves #1409.
Resolves #1410 (PR).

bin/get_gfs_status.pl

@@ -75,7 +75,7 @@
         my $url         = sprintf( qq{https://ftp.ncep.noaa.gov/%s}, $dir );
         my $res         = $ua->get($url);
         my $raw_listing = $res->{content};
-        my @dirs        = ( $raw_listing =~ m/>(.+)\/</g );
+        my @dirs        = ( $raw_listing =~ m/>(gfs.\d{8})\/</g );
         if ( not @dirs ) {
             warn "!! No directories found via $url\n";
         }