fix: switch to yarn for CI

Author: mike-north

.travis.yml

@@ -1,20 +1,15 @@
 language: node_js
 cache:
-  directories:
-    - ~/.npm
+  yarn: true
+yarn: true
 notifications:
   email: false
-install: npm install --skip-optional
+install: yarn install --no-lockfile --non-interactive
 node_js:
   - '10'
-  - '9'
   - '8'
-  - '6'
-after_success:
-  - nvm install 10
-  - nvm use 10
-  - npm install
-  - npm run travis-deploy-once "npm run semantic-release"
+script:
+  - yarn test && yarn travis-deploy-once "npm run semantic-release"
 branches:
   except:
     - /^v\d+\.\d+\.\d+$/

package.json

@@ -31,7 +31,7 @@
     "travis-deploy-once": "travis-deploy-once"
   },
   "devDependencies": {
-    "babel-core": "^7.0.0",
+    "babel-core": "^7.0.0-bridge",
     "@babel/preset-env": "^7.1.5",
     "@babel/preset-react": "^7.0.0",
     "@mike-works/js-lib-renovate-config": "2.0.0",

yarn.lock

@@ -2025,7 +2025,7 @@ babel-core@^6.0.0, babel-core@^6.24.1:
     slash "^1.0.0"
     source-map "^0.5.0"
 
-babel-core@^7.0.0:
+babel-core@^7.0.0-bridge:
   version "7.0.0-bridge.0"
   resolved "https://registry.yarnpkg.com/babel-core/-/babel-core-7.0.0-bridge.0.tgz#95a492ddd90f9b4e9a4a1da14eb335b87b634ece"
   integrity sha512-poPX9mZH/5CSanm50Q+1toVci6pv5KSRv/5TWCwtzQS5XEwn40BcCrgIeMFWP9CKKIniKXNxoIOnOq4VVlGXhg==