fix: react-native-git-upgrade/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-INFLIGHT-6095116

Author: snyk-bot

react-native-git-upgrade/package.json

@@ -24,7 +24,7 @@
     "promise": "^7.1.1",
     "rimraf": "^2.5.4",
     "semver": "^5.0.3",
-    "shelljs": "^0.7.5",
+    "shelljs": "^0.9.0",
     "yeoman-environment": "1.5.3"
   }
 }