Update Travis config and add lint task

Author: lukemelia

.travis.yml

@@ -18,16 +18,31 @@ env:
   global:
     # See https://git.io/vdao3 for details.
     - JOBS=1
+  matrix:
+    # we recommend new addons test the current and previous LTS
+    # as well as latest stable release (bonus points to beta/canary)
+    - EMBER_TRY_SCENARIO=ember-lts-2.12
+    - EMBER_TRY_SCENARIO=ember-lts-2.16
+    - EMBER_TRY_SCENARIO=ember-lts-2.18
+    - EMBER_TRY_SCENARIO=ember-release
+    - EMBER_TRY_SCENARIO=ember-beta
+    - EMBER_TRY_SCENARIO=ember-canary
+    - EMBER_TRY_SCENARIO=ember-default
 
 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:
-  - node_modules/.bin/ember try:each --skip-cleanup
+  - 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:one $EMBER_TRY_SCENARIO --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",