correct std docs: sqrt is elementwise

Author: stevengj

src/Statistics.jl

@@ -441,7 +441,7 @@ The algorithm returns an estimator of the generative distribution's standard
 deviation under the assumption that each entry of `itr` is a sample drawn from
 the same unknown distribution, with the samples uncorrelated.
 For arrays, this computation is equivalent to calculating
-`sqrt(sum((itr .- mean(itr)).^2) / (length(itr) - 1))`.
+`sqrt.(sum((itr .- mean(itr)).^2) / (length(itr) - 1))`.
 If `corrected` is `true`, then the sum is scaled with `n-1`,
 whereas the sum is scaled with `n` if `corrected` is
 `false` with `n` the number of elements in `itr`.