Install yarn on OSX by hand and update lock file

.travis.yml

@@ -142,6 +142,7 @@ before_install:
     if [[ "${TRAVIS_OS_NAME}" == "osx" ]]; then
       export JOBS=$((`sysctl -n hw.ncpu` + 1))
       sudo mdutil -i off /
+      npm install -g yarn
     fi
   - echo "Using ${JOBS} jobs"
   - yarn install --ignore-scripts

package.json

@@ -60,6 +60,7 @@
     "docbox": "^1.0.2",
     "documentation": "^4.0.0-beta.18",
     "eslint": "^2.4.0",
+    "react-dom": "^15.4.2",
     "tape": "^4.2.2",
     "uglifyjs": "^2.4.10"
   },