Ability to set the Content-Type header

Author: awwa

README.md

@@ -27,7 +27,7 @@ gem install ruby_http_client
 ```ruby
 require 'ruby_http_client'
 global_headers = {'Authorization' => 'Basic XXXXXXX' }
-client = SendGrid::Client(host: 'base_url', request_headers: global_headers)
+client = SendGrid::Client.new(host: 'base_url', request_headers: global_headers)
 client.your.api._(param).call.get
 puts response.status_code
 puts response.body
@@ -39,7 +39,7 @@ puts response.headers
 ```ruby
 require 'ruby_http_client'
 global_headers = {'Authorization' => 'Basic XXXXXXX' }
-client = SendGrid::Client(host: 'base_url', request_headers: global_headers)
+client = SendGrid::Client.new(host: 'base_url', request_headers: global_headers)
 query_params = { 'hello' => 0, 'world' => 1 }
 request_headers = { 'X-Test' => 'test' }
 data = { 'some' => 1, 'awesome' => 2, 'data' => 3}

lib/ruby_http_client.rb

@@ -148,7 +148,7 @@ def build_request(name, args)
       request = net_http.new(uri.request_uri)
       request = build_request_headers(request)
       request.body = @request_body.to_json if @request_body
-      if request.body
+      if request.body && !@request_headers.has_key?('Content-Type')
         request['Content-Type'] = 'application/json'
       elsif !request.body and (name.to_s == "post")
         request['Content-Type'] = ''