Add Salt 2018.3 tests

Change-Id: I12eb3de4ffd0981cfc51a11aeadbd9df458407aa
diff --git a/.travis.yml b/.travis.yml
index a08c030..20efff9 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