Add Salt 2018.3 tests

Change-Id: Iededdf61b9fb99a00e5448e1b97e790336ad34b3
diff --git a/.travis.yml b/.travis.yml
index 014c0c7..c4efd76 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,9 +17,11 @@
   - bundle install
 
 env:
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2016.3 SUITE=client
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2017.7 SUITE=client
-  # - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-bionic-salt-2017.7 SUITE=client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2016.3 SUITE=client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=client
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=client
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=client
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=client
 
 before_script:
   - set -o pipefail