Update travis secure key to re-enable notifications in slack.

[lzhoucs]

Type: feature

The following has been addressed in the PR:

• [ ] There is a related issue
• [x] All code matches the style guide
• [ ] Unit or Functional tests are included in the PR

Description:

It seems travis secure key has been out dated because we stopped receiving notifications in slack at some point. This change updates the key and re-enables notifications.