chore(package): update execa to version 3.4.0

Closes #89

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
   },
   "devDependencies": {
     "async-to-gen": "^1.3.3",
-    "execa": "^1.0.0",
+    "execa": "^3.4.0",
     "fixturez": "^1.1.0",
     "husky": "^1.2.0",
     "jest": "^23.6.0",