Add update endpoint for segments

[rreinhardt9]

https://translation.io/docs/api#segments-update

Add an endpoint and tests for updating a segment. We'll need to introduce a "patch" http verb method to our request object. Some inspiration for that could be:

https://github.com/lessonly/seismic_api/blob/8725dd68889e6db1a6e027498a731a568501bd7d/lib/seismic_api/request.rb#L61-L73