Json keyword misspelled in all ActC yaml files

[e-backmark-ericsson]

Description

All versions of yaml files for EiffelActivityCanceledEvent has a misspelling on 'additonalProperties'. It should be 'additionalProperties'.
See for example https://github.com/eiffel-community/eiffel/blob/master/definitions/EiffelActivityCanceledEvent/1.0.0.yml#L47
This results in wrongly generated Json schemas for ActC, see for example: https://github.com/eiffel-community/eiffel/blob/master/schemas/EiffelActivityCanceledEvent/1.0.0.json#L155

Motivation

We need to have syntactically correct json schemas

Exemplification

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Benefits

We need to have syntactically correct json schemas

Possible Drawbacks

What to do with old versions of this event?

[magnusbaeck]

Is this something that happened in the conversion of the schemas to the YAML format or has the problem been around forever?

[e-backmark-ericsson]

It was introduced in January 2017 through #86