Update .travis.yml to run older Ember scenarios.

And also use `yarn` instead of `npm`...

Author: Robert Jackson

.travis.yml

@@ -12,8 +12,7 @@ addons:
   chrome: stable
 
 cache:
-  directories:
-    - $HOME/.npm
+  yarn: true
 
 env:
   global:
@@ -31,24 +30,36 @@ jobs:
     - stage: "Tests"
       name: "Tests"
       script:
-        - npm run lint:hbs
-        - npm run lint:js
-        - npm test
+        - yarn lint:hbs
+        - yarn lint:js
+        - yarn test
+    - name: "Floating Dependencies"
+      install:
+        - yarn install --no-lockfile --non-interactive
+      script:
+        - yarn test
+
 
     # we recommend new addons test the current and previous LTS
     # as well as latest stable release (bonus points to beta/canary)
     - stage: "Additional Tests"
-      env: EMBER_TRY_SCENARIO=ember-lts-2.16
+      env: EMBER_TRY_SCENARIO=ember-1.13
+    - env: EMBER_TRY_SCENARIO=ember-lts-2.4
+    - env: EMBER_TRY_SCENARIO=ember-lts-2.8
+    - env: EMBER_TRY_SCENARIO=ember-lts-2.12
+    - env: EMBER_TRY_SCENARIO=ember-lts-2.16
     - env: EMBER_TRY_SCENARIO=ember-lts-2.18
     - env: EMBER_TRY_SCENARIO=ember-release
     - env: EMBER_TRY_SCENARIO=ember-beta
     - env: EMBER_TRY_SCENARIO=ember-canary
     - env: EMBER_TRY_SCENARIO=ember-default-with-jquery
 
 before_install:
-  - npm config set spin false
-  - npm install -g npm@4
-  - npm --version
+  - curl -o- -L https://yarnpkg.com/install.sh | bash
+  - export PATH=$HOME/.yarn/bin:$PATH
+
+install:
+  - yarn install --non-interactive
 
 script:
-  - node_modules/.bin/ember try:one $EMBER_TRY_SCENARIO
+  - yarn ember try:one $EMBER_TRY_SCENARIO