chore(package): update execa to version 0.6.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -61,7 +61,7 @@
     "eslint-plugin-promise": "^3.4.0",
     "eslint-plugin-require-path-exists": "^1.1.5",
     "eslint-plugin-standard": "^2.0.1",
-    "execa": "^0.5.0",
+    "execa": "^0.6.0",
     "husky": "^0.12.0",
     "np": "^2.12.0",
     "nyc": "^10.0.1-candidate.0",