Add Salt 2018.3 tests

Change-Id: Ibf6f47b610a40def4f7c6403155f217b9545fa74
diff --git a/.travis.yml b/.travis.yml
index 2c123b5..cae612d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,9 +20,11 @@
   - bundle install
 
 env:
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2016.3 SUITE=telegraf-agent
-  - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-xenial-salt-2017.7 SUITE=telegraf-agent
-  # - PLATFORM=epcim/salt-formulas:saltstack-ubuntu-bionic-salt-2017.7 SUITE=telegraf-agent
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2016.3 SUITE=telegraf-agent
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=telegraf-agent
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=telegraf-agent
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=telegraf-agent
+  # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=telegraf-agent
 
 before_script:
   - set -o pipefail