site.conf: use single quotes for strings

For consistency, use single quotes for all strings in the site
configuration.

site.conf

@@ -65,7 +65,7 @@
 		branch => 'stable',
 		branches => {
 			stable => {
-				name => "stable",
+				name => 'stable',
 				mirrors => ['http://[fdef:ffc0:3dd7::ffff:0]/stable/'],
 				probability => 0.08,
 				good_signatures => 2,
@@ -80,7 +80,7 @@
 
 	simple_tc => {
 		mesh_vpn => {
-			ifname => "mesh-vpn",
+			ifname => 'mesh-vpn',
 			enabled => 0,
 			limit_egress => 200,
 			limit_ingress => 3000,