package/copas: update the upstream URL in Config.in

Update the upstream URL in the help text in Config.in. This
addresses the 'Invalid(406)' URL status in the package stats
web page output.

Signed-off-by: Mark Corbin <mark@dibsco.co.uk>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/copas/Config.in

@@ -8,4 +8,4 @@ config BR2_PACKAGE_COPAS
 	  servers. But it also features timers and client support for
 	  http(s), ftp and smtp requests.
 
-	  http://www.keplerproject.org/copas/
+	  http://keplerproject.github.io/copas/