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

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-LODASH-6139239

react-native-git-upgrade/package.json

@@ -25,6 +25,6 @@
     "rimraf": "^2.5.4",
     "semver": "^5.0.3",
     "shelljs": "^0.7.5",
-    "yeoman-environment": "1.5.3"
+    "yeoman-environment": "1.6.0"
   }
 }