Change #hacknight topic regularly

[agarzola]

Every Wednesday evening, change the topic on #hacknight to reflect the new date (keep everything else as-is). Likewise, create an issue on the website repo to change the date on the announcement we have on the website.

[DigTK]

https://api.slack.com/methods/channels.setTopic

I bet we can spin up a scheduled task somewhere that grabs the next date and send a request to that API