Update unified-types.md

[shitpoet]

Add phrase:

Note that Long to Float conversion is deprecated in new versions of Scala, because of the potential precision lost.

[bishabosha]

Thanks! While this is technically correct, perhaps its better to fix the example to another conversion that isn't lossy

[som-snytt]

I had to visit the web page to understand the issue. I think bishabosha's previous edit .toFloat breaks the text, which is trying to show how easy and wonderful numeric widening is. Instead, it should show the types and also trumpet Scala's "gun buy-back program" for footguns.