fix(package): update execa to version 2.0.3

Closes #16

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
     "test": "jest --coverage"
   },
   "dependencies": {
-    "execa": "^1.0.0",
+    "execa": "^2.0.3",
     "meow": "^5.0.0",
     "p-map-series": "^1.0.0",
     "travis-or-circle": "^1.0.2"