use jobs instead of matrix. as only latest is tested, remove VERSION

.travis.yml

@@ -12,7 +12,7 @@ before_script:
 
 script:
   - cd "$dir"
-  - travis_wait docker build --build-arg VERSION=${VERSION} -t ejabberd/ecs:travis-${VERSION} .
+  - travis_wait docker build --build-arg VERSION=latest -t ejabberd/ecs:travis-latest .
   - docker images
   - travis_retry docker run --name ejabberd -d -p 5222:5222 ejabberd/ecs && sleep 60
   - docker ps
@@ -22,11 +22,11 @@ script:
 notifications:
   email: false
 
-matrix:
+jobs:
   allow_failures:
-    - env: VERSION=latest VARIANT=ecs
-    - env: VERSION=latest VARIANT=mix
+    - env: VARIANT=ecs
+    - env: VARIANT=mix
 
 env:
-  - VERSION=latest VARIANT=ecs
-  - VERSION=latest VARIANT=mix
+  - VARIANT=ecs
+  - VARIANT=mix