component/libcap-ng: Use reliable source

SSL certificate of people.redhat.com has bad chain, which results with failed
downloads.

component/libcap-ng/buildout.cfg

@@ -8,7 +8,7 @@ parts = libcap-ng
 [libcap-ng]
 recipe = slapos.recipe.cmmi
 shared = true
-url = https://people.redhat.com/sgrubb/libcap-ng/libcap-ng-0.8.2.tar.gz
+url = http://sources.buildroot.net/libcap-ng/libcap-ng-0.8.2.tar.gz
 md5sum = faf1ef766cf068ad1aba4008ced665f7
 location = @@LOCATION@@
 configure-options =