chore: pin react to 15.4.2

Author: greenkeeper[bot]

package.json

@@ -89,7 +89,7 @@
     "jsdom-global": "^2.1.0",
     "mocha": "^3.2.0",
     "nyc": "^10.0.0",
-    "react": "^15.3.2",
+    "react": "15.4.2",
     "react-addons-test-utils": "^15.3.2",
     "react-dom": "^15.3.2",
     "react-hot-loader": "^3.0.0-beta.2",