Remove unnecessary Content-Type header for when request body is empty

Author: disco-falsetta

lib/duo_api.rb

@@ -61,8 +61,6 @@ def request(method, path, params = {}, additional_headers = nil)
     if params_go_in_body
       request['Content-Type'] = 'application/json'
       request.body = body
-    else
-      request['Content-Type'] = 'application/x-www-form-urlencoded'
     end
 
     Net::HTTP.start(