sylpheed: fix upstream URL

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/sylpheed/Config.in

@@ -4,4 +4,4 @@ config BR2_PACKAGE_SYLPHEED
 	help
 	  lightweight and user-friendly e-mail client.
 
-	  http://sylpheed.sraoss.jp/sylpheed/v2.4
+	  http://sylpheed.sraoss.jp/en/