Change options[:test_clone] default to false

* Rails 4.1.0 handles the db:test:clone by 
  default, so if you are using a version of Rails
  older than 4.1.0, make sure you set
  options[:test_clone] to true.

* Modified README.rdoc to specify the new default
  value
Merge pull request #17 from jasonnoble/change_default_test_clone_option

removes deprecation warning for db:test:clone