Add Rakefile task for running rspec

Rakefile

@@ -1,6 +1,9 @@
-# Add your own tasks in files placed in lib/tasks ending in .rake,
-# for example lib/tasks/capistrano.rake, and they will automatically be available to Rake.
-
 require_relative 'config/application'
 
 Rails.application.load_tasks
+
+begin
+  require 'rspec/core/rake_task'
+  RSpec::Core::RakeTask.new(:spec)
+rescue LoadError
+end