fix(package): update execa to version 0.9.0

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
   "dependencies": {
     "@semantic-release/error": "^2.1.0",
     "debug": "^3.1.0",
-    "execa": "^0.8.0",
+    "execa": "^0.9.0",
     "lodash": "^4.17.4",
     "parse-json": "^4.0.0"
   },