Small Ruby 2.7 + changelog fixes

[nbulaj]

As from the title: small fix for kwargs in Grape::Exceptions::Validation class and typo fix in changelog.

[grape-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

Generated by 🚫 danger

[dblock]

Is this something that fixes a bug? I mean is there a test that can be written that fails without this change?

[nbulaj]

No-no, it's not a bugfix :) It's one more fix for Ruby 2.7 / 3.0 kwargs deprecatiob messages that eas somehow lost in #1949 . Without it you'll just see a warning in the stdout. And a typo fix in the changelog. So no additional specs required, just regression that already exist

[anatol]

We are looking at ruby2.7 issues in gitlab and one we found is https://gitlab.com/gitlab-org/gitlab/issues/194348 Could it be related to the fix above? Or you think the issue is somewhere else?

[dblock]

Maybe. I would check against HEAD, but also note #1957.

[nbulaj]

@anatol I checked GitLab issue and don't sure I understood the source of the issue. I mean I can't find in the logs who exactly produced an error you faced (GitLab internals? rack oauth2? Grape?).

This PR and #1949 add double-splat operator in places where Grape uses kwargs in method definition. It could be a source of the issue, but first it would be great to find the line of the code which produces it