hotfix: yarn cache clean for CI

.travis.yml

@@ -10,8 +10,9 @@ before_install:
   - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.12.3
   - export PATH="$HOME/.yarn/bin:$HOME/.config/yarn/global/node_modules/.bin:$PATH"
 cache:
-  yarn: false
+  yarn: true
 install:
+  - yarn cache clean
   - yarn install
   - cd embark-ui && yarn install && cd ..
   - git status && test -z "$(git status --porcelain)"

appveyor.yml

@@ -12,6 +12,7 @@ install:
   - rm yarn-1.12.3.msi
   - node --version
   - yarn --version
+  - yarn cache clean
   - yarn install
   - cd embark-ui && yarn install && cd ..
   - git status && node -e "process.exit(require('child_process').execSync('git status --porcelain').toString().trim()===''?0:1)"