There is a Equal Sign missing in Line 323 of media_mattermost.xml. It should be between "triggerid" and "{1}".

Steps to reproduce:

1. Follow Tutorial to setup Mattermost integration
2. Wait until a trigger fires
3. Try to click the link in the title

Result:
When inspecting the link you clearly see the missing equal sign.
 
When Clicking you get the following Error:

Expected:
You should see the correct page: