fix(Modal): fix positioning when "as" prop is a component

[trevorharwell]

I found that when I use <Modal as={SomeComponent} /> in React 16, the modal positioning broke. This is an easy and straight forward way to remedy the problem. Let me know if there is an alternative approach that I should be taking.

Re Testing: I didn't see any tests that covered this particular function so I didn't add any. If that is desired I can try to figure something out.

[welcome]

💖 Thanks for opening this pull request! 💖

Here is a list of things that will help get it across the finish line:

• Run yarn lint locally to catch formatting errors. This will fix some errors automatically, commit and push any changes.
• Run yarn test locally to catch errors. This ensures all components still behave as they should.
• Run yarn start to run the doc site locally and try a few pages, ensuring everything is in good working order.
• Include tests when adding/changing behavior.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codecov-io]

Codecov Report

Merging #2623 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2623   +/-   ##
=======================================
  Coverage   99.74%   99.74%           
=======================================
  Files         160      160           
  Lines        2751     2751           
=======================================
  Hits         2744     2744           
  Misses          7        7

Impacted Files	Coverage Δ
src/modules/Modal/Modal.js	100% <ø> (ø)	⬆️

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[trevorharwell]

Now that I have had some time to think about this, I believe this could be easily solved by wrapping the content element in a Ref component and using that to set the ref. Would that be something you guys would approve?

[layershifter]

@trevorharwell thanks for PR 👍

In fact, we have a quite stale #2306, that should solve this problem for all components. As current solution, we can accept PR that will use <Ref /> for refs and add a TODO for future removal.

[trevorharwell]

@layershifter Thanks for getting back to me. I updated the PR per your request. Let me know if there is anything else I should do.

FYI we use SUIR for a large scale web application at my company and we love it! Thanks for such a great library!

[levithomason]

@layershifter this looks OK to me for a short-term fix, merge at will. Perhaps we should add these TODOs to #2306 so we remember to clean them up.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[levithomason]

Released in semantic-ui-react@0.79.0.