[6.0] 4cd71a88d duh, travis-ci needs to join for this to work

[Dridi Boukelmoune]

commit 4cd71a88d222275eabf50dbce21923c247b84792
Author: Federico G. Schwindt <fgsch at lodoss.net>
Date:   Mon Apr 23 13:06:51 2018 +0100

    duh, travis-ci needs to join for this to work

diff --git a/.travis.yml b/.travis.yml
index 8a741f6bc..76a6f705a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,7 +31,6 @@ notifications:
       - "irc.linpro.no#varnish-hacking"
     on_success: change
     use_notice: true
-    skip_join: true
 before_install:
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
       brew update;