formatting: add missing newline stable

formatting: add missing newline

Differential Revision: https://phab.mercurial-scm.org/D8509

--- a/mercurial/utils/procutil.py	Mon Apr 27 01:39:22 2020 +0200
+++ b/mercurial/utils/procutil.py	Fri May 08 01:19:48 2020 +0200
@@ -612,6 +612,7 @@
                     # We use a thread to make the overhead tiny.
                     def _do_wait():
                         os.waitpid(pid, 0)
+
                     threading.Thread(target=_do_wait, daemon=True).start()
                     return
                 # Parent process