Update Travis config and add lint task

.travis.yml

@@ -21,13 +21,18 @@ env:
 
 matrix:
   fast_finish: true
+  allow_failures:
+    - env: EMBER_TRY_SCENARIO=ember-canary
 
 before_install:
   - curl -o- -L https://yarnpkg.com/install.sh | bash
   - export PATH=$HOME/.yarn/bin:$PATH
 
 install:
-  - yarn install --no-lockfile --ignore-engines --non-interactive
+  - yarn install --no-lockfile --non-interactive
 
 script:
+  - yarn lint:js
+  # Usually, it's ok to finish the test scenario without reverting
+  #  to the addon's original dependency state, skipping "cleanup".
   - node_modules/.bin/ember try:each --skip-cleanup

package.json

@@ -16,7 +16,8 @@
     "build": "ember build",
     "start": "ember serve",
     "deploy": "ember github-pages:commit --message \"Deploy gh-pages from commit $(git rev-parse HEAD)\"; git push; git checkout -",
-    "test": "ember try:each"
+    "test": "ember try:each",
+    "lint:js": "eslint ./*.js app config lib server tests"
   },
   "dependencies": {
     "ember-cli-babel": "^6.12.0",