Update 160604-build-first-slack-bot-python.markdown

[emmacallahan]

The changes are necessary for slackclient v2.x

[mattmakai]

thanks @emmacallahan. no other changes necessary to make this work with v2.x?

[emmacallahan]

From what I understand, there are a few more steps to make it work.
There are changes to the RTM API. See here https://github.com/slackapi/python-slackclient/wiki/Migrating-to-2.x

When I get it working, I will add it here as well.

[mattmakai]

ok thank you @emmacallahan! add the changes to this pull request when they're ready, I will take a look and test then merge when appropriate.