Enable warnings in the spec Rake task

Author: chastell

Rakefile

@@ -4,6 +4,7 @@ require 'rake/testtask'
 Rake::TestTask.new do |t|
   t.name = 'spec'
   t.pattern = 'spec/**/*_spec.rb'
+  t.warning = true
 end
 
 task default: :spec