Upgrade execa 3.4.0 -> 4.0.0

Author: ehmicky

package-lock.json

@@ -62,7 +62,7 @@
   "devDependencies": {
     "@ehmicky/dev-tasks": "^0.30.71",
     "ava": "^2.4.0",
-    "execa": "^3.4.0",
+    "execa": "^4.0.0",
     "gulp": "^4.0.2",
     "has-ansi": "^4.0.0",
     "husky": "^3.1.0",