ci: switch to yarn

.yarnclean

@@ -0,0 +1,45 @@
+# test directories
+__tests__
+test
+tests
+powered-test
+
+# asset directories
+docs
+doc
+website
+images
+assets
+
+# examples
+example
+examples
+
+# code coverage directories
+coverage
+.nyc_output
+
+# build scripts
+Makefile
+Gulpfile.js
+Gruntfile.js
+
+# configs
+appveyor.yml
+circle.yml
+codeship-services.yml
+codeship-steps.yml
+wercker.yml
+.tern-project
+.gitattributes
+.editorconfig
+.*ignore
+.eslintrc
+.jshintrc
+.flowconfig
+.documentup.json
+.yarn-metadata.json
+.travis.yml
+
+# misc
+*.md

lerna.json

@@ -1,7 +1,7 @@
 {
   "lerna": "2.4.0",
-  "packages": [
-    "packages/*"
-  ],
+  "npmClient": "yarn",
+  "useWorkspaces": true,
+  "packages": ["packages/*"],
   "version": "3.2.2"
 }