Preserve state of random number generator in .onAttach()

Currently .onAttach() will change the state of a users random number generator:

Lines 1 to 2 in d143826

    
           .onAttach <- function(...) { 
        
             if (!interactive() || stats::runif(1) > 0.2) return()

Not a bug per se but would you consider a change to preserve it?

For reference I believe {ggplot2} was updated to use withr::with_preserve_seed() for this reason.

Thanks for the suggestion, I've created a PR (#955) for this.

	.onAttach <- function(...) {
	if (!interactive() \|\| stats::runif(1) > 0.2) return()