chore(package): update execa to version 2.1.0

Closes #16

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "eslint-config-xo": "^0.24.2",
     "eslint-plugin-json": "^1.2.1",
     "eslint-plugin-prettier": "^2.6.2",
-    "execa": "^1.0.0",
+    "execa": "^2.1.0",
     "husky": "^0.14.3",
     "jest": "^23.5.0",
     "jest-cli": "^23.5.0",