Add Salt 2018.3 tests

Change-Id: I0e972ff4c1bffe5825de7a2768a63bf29d39e0c1
diff --git a/.travis.yml b/.travis.yml
index b19ef0c..31035b2 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=server
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2017.7 SUITE=server
-  # - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-bionic-salt-2017.7 SUITE=server
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2016.3 SUITE=server
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=server
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=server
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=server
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=server
 
 before_script:
   - set -o pipefail