reformat for :accept header

Reformatting example to better indicate the `:accept` header is sent as a separate parameter. Before, it looked like it was part of the same hash. 
Merge pull request #235 from aaronpk/master

Reformatting to better indicate how to send `:accept` header

See: http://rubydoc.info/gems/rest-client/1.6.7/RestClient.post