Use IPC::Run3 rather than IPC::Open3

IPC::Open3 is recommended by Perl::Critic, but it's a relatively
low-level tool that requires system select() calls and careful
attention to buffering/blocking, among other things. It looks like it's
great if you need fine-tuned detail like that, but in this case, I
don't, I just need something better than system() that will capture both
stdout and stderr from a call.

IPC::Run3 is by the same author and much better suited to this purpose.