Fix a typo

[rrthomas]

Fixes #1152.

[rrthomas]

A one-character fix.

[ehmicky]

Thanks @rrthomas. Just a small issue.

[rrthomas]

Thanks, I didn't spot that the \ was correct, not a typo, and the close paren was simply missing. This is the sort of issue where I think it's probably better for the upstream maintainers to take two minutes to fix a bug rather than 5 minutes to interact with the reporter. My perspective is that I'm using execa as part of other libre projects, and I think we'll all have more fun and give more to the world if we spend our time on our own projects in this case. I understand of course that the one thing we all lack is compensation and/or assistance, and also that execa and other projects you work on are wildly popular, unlike the projects I work on, so the load on your may well be correspondingly greater.