Add Salt 2018.3 tests

Change-Id: I699d58f268ef3dd7471ecf74ed01def35089d7fc
diff --git a/.travis.yml b/.travis.yml
index c1c100f..0962f7f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,8 +24,11 @@
   - bundle install
 
 env:
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2016.3 SUITE=debmirror-client
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2017.7 SUITE=debmirror-client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2016.3 SUITE=debmirror-client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=debmirror-client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=debmirror-client
+#  - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=debmirror-client
+#  - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=debmirror-client
 
 before_script:
   - set -o pipefail