Add pidfile option

spec/config_spec.rb

@@ -2,10 +2,11 @@ require "spec_helper"
 
 describe Crono::Config do
   describe "#initialize" do
-    it "should initialize schedule" do
+    it "should initialize with default configuration options" do
       @config = Crono::Config.new
       expect(@config.cronotab).to be Crono::Config::CRONOTAB
       expect(@config.logfile).to be Crono::Config::LOGFILE
+      expect(@config.pidfile).to be Crono::Config::PIDFILE
       expect(@config.daemonize).to be false
     end
   end