Update audio.rb

Author: Shpigford

lib/openai/audio.rb

@@ -11,5 +11,9 @@ def transcribe(parameters: {})
     def translate(parameters: {})
       @client.multipart_post(path: "/audio/translations", parameters: parameters)
     end
+
+    def speech(parameters: {})
+      @client.json_post(path: "/audio/speech", parameters: parameters)
+    end
   end
 end