Updated Handlebars Expressions Link

Old link was broken (404).

Author: jpappendick

src/connections/destinations/catalog/slack/index.md

@@ -75,7 +75,7 @@ If you would like to have specific events be sent to a particular channel (#chan
 
 
 ### Event Templates
-Event templates also use [Handlebars expressions](http://handlebarsjs.com/expressions.html) syntax. Make sure you reference the spec for the [Track method](/docs/connections/spec/track/) and [common object](/docs/connections/spec/common/). `Track` events will trigger a Slack message with the following default template:
+Event templates also use [Handlebars expressions](https://handlebarsjs.com/guide/expressions.html) syntax. Make sure you reference the spec for the [Track method](/docs/connections/spec/track/) and [common object](/docs/connections/spec/common/). `Track` events will trigger a Slack message with the following default template:
 
 `'\{{name}} did \{{event}}.'`