Upgrade to asio 1.12.1 (for compatibility with OpenSSL 1.1.0)

[jcheng5]

Hi Dirk,

My team has a new R package for WebSocket clients that depends on asioheaders. A user reported that it couldn't be installed on recent rocker images: rstudio/websocket#15

Here is the underlying asio issue: chriskohlhoff/asio#184

No problems reported with R CMD check --as-cran on iptools (both CRAN and GitHub versions), which is the only direct reverse dependency on CRAN.

Please let me know if you need any other information from me--thanks!

[eddelbuettel]

That rocks.

I was actually going over dozens of repos of mine this weekend (for a benign Travis use upgrade) and also noticed the new Asio and planned to do this. Your PR makes it a lot easier :)

As you know, CRAN is currently closed so there is not way to rush this but I think I will push this as soon as they reopen. Would you need it / would it help if it were drat-able? I could push it into one of mine...

[jcheng5]

Thanks for merging! No need to drat, I don't think--and our stuff isn't on CRAN yet anyway, so if you submit next week or whenever that'd be fine with me.

[eddelbuettel]

This is now on CRAN. Thanks again for the clean PR.