[3.5] solve Exercise 1

 * add spec first
 * add routes to config/routes.rb
 * add action to controller
 * add template
 * also fix a typo
[3.5] solve Exercise 2

 * modify rspec to use let method
[3.6.1] add bundler_stubs setting
[3.6.3] add guard-rspec
[3.6.3] add spork settings