linkfile: improve the URL regex

By requiring a "non-word" letter or start-of-line before the URL

roffit

@@ -10,7 +10,7 @@
 # Author:  Daniel Stenberg <daniel@haxx.se>
 # Web:     https://daniel.haxx.se/projects/roffit
 
-my $version = "0.11";
+my $version = "0.12";
 
 use strict;
 #use warnings;
@@ -219,7 +219,7 @@ sub linkfile {
             }
 
             # convert https://, http:// and ftp:// URLs to <a href> links
-            $field =~ s/(^|[\"\s])((?:https|http|ftp):\/\/[a-z0-9\-._~%:\/?\#\[\]\@!\$&'()*+,;=]+)/$1<a href=\"$2\">$2<\/a>/gi;
+            $field =~ s/(^|\W)((https|http|ftp):\/\/[a-z0-9\-._~%:\/?\#\[\]\@!\$&'()*+,;=]+)/$1<a href=\"$2\">$2<\/a>/gi;
 
             # convert (uppercase only) "RFC [number]" to a link
             $field =~ s/(^|[\"\s])RFC ?(\d+)/$1<a href=\"http:\/\/www.ietf.org\/rfc\/rfc$2.txt\">RFC $2<\/a>/g;