Add Salt 2018.3 tests

Change-Id: Ic32cd07f358c7e20951ffc3146c1c58ce709d398
diff --git a/.travis.yml b/.travis.yml
index 5457048..cf56201 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,9 +17,12 @@
   - bundle install
 
 env:
-    - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2016.3 SUITE=single
-    - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2017.7 SUITE=single
-#    - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-bionic-salt-2017.7 SUITE=single
+    - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2016.3 SUITE=single
+    - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=single
+    - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=single
+#    - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=single
+#    - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=single
+
 before_script:
   - set -o pipefail
   - make test | tail