Gentoo: Set systemd as default provider

Systemd is available on Gentoo since a long time (although Gentoo
supports multiple init systems). This change marks the provider as
default for Gentoo.

lib/puppet/provider/service/systemd.rb

@@ -26,6 +26,7 @@
   defaultfor :operatingsystem => :ubuntu
   notdefaultfor :operatingsystem => :ubuntu, :operatingsystemmajrelease => ["10.04", "12.04", "14.04", "14.10"] # These are using upstart
   defaultfor :operatingsystem => :cumuluslinux, :operatingsystemmajrelease => ["3", "4"]
+  defaultfor :operatingsystem => :gentoo
 
   def self.instances
     i = []