uses include type class declaration

previous behavior used class { 'stdlib::stages':} which isn't singleton and could cause duplication resource declaration on the stages class.

Since many community modules work by calling 'include stdlib' we should make stdlib's include of stages singleton as well.

manifests/init.pp

@@ -14,7 +14,5 @@
 # Requires: nothing
 #
 class stdlib {
-
-  class { 'stdlib::stages': }
-
+  include stdlib::stages
 }