Provide link to discord in Community links

The page linked to Slack.  Our current platform for communication is Discord.

@locks Here you go

Author: madnificent

_posts/2014-04-05-overview.md

@@ -101,7 +101,7 @@ improve your quality of life as an Ember developer.
 
 Talk to us here:
 
-* Slack: [Get your invite](https://ember-community-slackin.herokuapp.com)
+* Discord: [Get your invite](https://discordapp.com/invite/zT3asNS)
 * Issues: [ember-cli/issues](https://github.com/ember-cli/ember-cli/issues)
 
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