Remove mention of rake test
Remove mention of rake test

- Note that the default rake RSpec task is provided by pliny-template.
- This will likely stop being a concern when #83 is merged and the
  documentation for pliny-template is split out of this README.

hayduke19us/pliny,fdr/pliny,hayduke19us/pliny,fdr/pliny,hayduke19us/pliny,fdr/pliny,interagent/pliny,interagent/pliny,interagent/pliny