Don't test on trusty due to missing aptly package

Change-Id: I14e75a1baf26bf376f99b608db092417ce7825f1
diff --git a/.travis.yml b/.travis.yml
index 7a77247..18742e0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,7 +17,6 @@
   - bundle install
 
 env:
-    - PLATFORM=trevorj/salty-whales:trusty
     - PLATFORM=trevorj/salty-whales:xenial
 
 before_script: