Use yarn

Author: hzalaz

circle.yml

@@ -1,16 +1,23 @@
 machine:
   node:
     version: v6.10.0
+  environment:
+    PATH: "${PATH}:${HOME}/${CIRCLE_PROJECT_REPONAME}/node_modules/.bin"
+dependencies:
+  override:
+    - yarn
+  cache_directories:
+    - ~/.cache/yarn
 test:
   pre:
-    - npm run build
-    - npm run lint
+    - yarn run build
+    - yarn run lint
   override:
-    - npm run ci:test:
+    - yarn run ci:test:
         environment:
           MOCHA_FILE: $CIRCLE_TEST_REPORTS/junit/test-results.xml
   post:
-    - npm run ci:coverage
+    - yarn run ci:coverage
 general:
   artifacts:
     - build