Update copyright date

Author: Jeff Ammons

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2015 Slack Technologies, Inc
+Copyright (c) 2015-2016 Slack Technologies, Inc
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

slackclient/_slackrequest.py

@@ -29,4 +29,4 @@ def do(token, request="?", post_data=None, domain="slack.com"):
         post_data['token'] = token
         files = {'file': post_data.pop('file')} if 'file' in post_data else None
 
-        return requests.post(url, data=post_data, files=files)
+        return requests.post(url, data=post_data, files=files)