Concurrency sample uses deprecated `future` function

[kubukoz]

val x = future { someExpensiveComputation() }
val y = future { someOtherExpensiveComputation() }
val z = for (a <- x; b <- y) yield a*b
for (c <- z) println("Result: " + c)
println("Meanwhile, the main thread goes on!")

from the sources:

@deprecated("use `Future { ... }` instead", "2.11.0")
// removal planned for 2.13.0
def future[T](body: =>T)

The future usage should probably be replaced with Future { } in this example (and its description). If you think it's a good idea, I can prepare a PR in no time :)

[SethTisue]

yes please!

[kubukoz]

I can see that the correct version is used in _includes/bullet-concurrency-distribution.html since #642 - why are there two places for these snippets?

Anyways, I should have a PR with a fix for this within minutes :)

[kubukoz]

It's ready in #878 :)