[JS] putThing throws error when updating an existing Thing

[vhdirk]

According to the docs, a PUT request for an existing Thing will have ditto respond with status 204 and an empty body.
The JS client SDK, however, always expects body: https://github.com/eclipse/ditto-clients/blob/master/javascript/lib/api/src/client/request-factory/request-sender.ts#L48

[ffendt]

Good catch! Do you want to provide a PR for that?