Add rake task to check cronotab.rb syntax

lib/tasks/crono_tasks.rake

@@ -1,6 +1,10 @@
 module Crono
   def self.load_cronotab
-    require File.join(Rails.root, Config::CRONOTAB)
+    cronotab_path = ENV['CRONOTAB'] || (defined?(Rails) &&
+                      File.join(Rails.root, cronotab_path))
+    fail 'No cronotab defined' unless cronotab_path
+    puts "Load cronotab #{cronotab_path}"
+    require cronotab_path
   end
 end
 
@@ -12,4 +16,11 @@ namespace :crono do
     current_job_ids = Crono.scheduler.jobs.map(&:job_id)
     Crono::CronoJob.where.not(job_id: current_job_ids).destroy_all
   end
+
+  desc 'Check cronotab.rb syntax'
+  task check: :environment do
+    Crono.scheduler = Crono::Scheduler.new
+    Crono.load_cronotab
+    puts 'Syntax ok'
+  end
 end