Update _package.json

[JosephSKh]

Change "mongoose": "4.1.2" to "mongoose": "^4.1.2" Cause: DeprecationWarning: open() is deprecated in mongoose >= 4.11.0, use openUri() instead, or set the useMongoClient option if using connect() or createConnection().

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• [x] The generator's tests pass (generator-angular-fullstack$ npm test)