Bug#831228: update-flashplugin-nonfree references wrong version

[Juanjo Benages]

Changing the user agent in get-upstream-version.pl to the Firefox one fixes
this problem

--- get-upstream-version(1).pl	2016-07-15 16:04:48.749385098 +0200
+++ get-upstream-version.pl	2016-07-15 16:09:09.439475962 +0200
@@ -31,8 +31,7 @@
 
 	{
 		local $/ = undef;
-		my $user_agent = "Mozilla/5.0 (X11; U; Linux $arch; en-us) AppleWebKit/531.2+ (KHTML, like Gecko)"
-			." Version/5.0 Safari/531.2+ Debian/squeeze (2.30.6-1) Epiphany/2.30.6";
+		my $user_agent = "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0";
 
 		open INPUT, "wget --no-check-certificate --tries=1 --user-agent=\"$user_agent\" -nv -qO - $url |" or die;
 		$page = <INPUT>;