Fix logic for checking type of object (directory or file)

[DenisaCG]

We need to fix the logic for checking if we are dealing with an object that is a directory or a simple file.

The current version relies on the directory name not including an extension as a suffix, in order to identify the directory object.

jupydrive-s3/src/s3contents.ts

Line 486 in f27e43b

const isDir: boolean = PathExt.extname(localPath) === '';

This logic should be replaced with a helping function that properly checks the type of object we are dealing with (e.g. by listing the contents given a path).