[ripple/rippled] Replace boost::unique_lock with std::unique_lock (#2617)

Sorry, I wasn’t clear. I’m recommending we eliminate the dependence on boost completely by replacing `boost::shared_mutex` with `std::shared_timed_mutex`. They are roughly equivalent. “shared_mutex” was renamed to “shared_timed_mutex” during the standardization process.

This post was last modified on July 6, 2018, 4:21 am