Modified json file make collectionExist return false about jsondb-core

[DataMirko]

There was a mistake in the json file. Data could not loaded correctly in the java Class field

[byronv5]

Each JsonDBTemplate corresponding to dbFilesLocationString must be a singleton. Otherwise, when a second thread creates a new JsonDBTemplate(...), calling the lock method will throw an OverlappingFileLockException exception. After the exception occurs, the corresponding data item in collectionsRef will be deleted. Subsequently, when calling collectionExists, it will return false. Ultimately, if we invoke createCollection, it will overwrite the original file, resulting in data deletion.