travis: Add Elm stage

.travis.yml

@@ -1,30 +1,38 @@
-language: go
 sudo: false
 
-addons:
-  apt:
-    packages:
-      - rpm
-
 env:
   global:
     - GO111MODULE=on
 
-install:
-  - go get golang.org/x/lint/golint
-  - make deps
-
+language: go
 go:
   - "1.11.x"
-  - "tip"
+  - "master"
+
+install:
+  - "go get golang.org/x/lint/golint"
+  - "make deps"
 
 jobs:
   include:
+    - stage: elm
+      install:
+        - "cd ui"
+        - "npm install"
+      script:
+        - "elm-format --validate ."
+        - "npm run build"
+      language: elm
+      elm: "0.19.0"
     - stage: deploy
-      script: etc/travis-deploy.sh
-      go: "1.11.x"
+      script: "etc/travis-deploy.sh"
+      addons:
+        apt:
+          packages:
+            - rpm
 
 stages:
   - test
+  - elm
   - name: deploy
     if: tag IS present