chore(package): update execa to version 0.6.0 (#702)

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -63,7 +63,7 @@
     "chai": "^3.5.0",
     "detect-node": "^2.0.3",
     "eslint-plugin-react": "^6.8.0",
-    "execa": "^0.5.0",
+    "execa": "^0.6.0",
     "expose-loader": "^0.7.1",
     "form-data": "^2.1.2",
     "fs-pull-blob-store": "^0.4.1",