Fix typos in scaffold files

[SamGuay]

As soon as a participant sub-* directory is added, the validator will do its job and validate the dataset and won't trigger errors in the files generated by dcm2bids_scaffold.

Though, two warnings should come up, which is good as people need to fill these up:

Warning 1: [Code 102] TOO_FEW_AUTHORS
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The Authors field of dataset_description.json should contain an array of fields - with one author per field. This was triggered based on the presence of only one author field. Please ignore if all contributors are already properly listed.

Warning 2: [Code 115] EMPTY_DATASET_NAME
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The Name field of dataset_description.json is present but empty of visible characters.

Closing #254

[arnaudbore]

GTG