fsmonitor: correct an error message Without the change, the error looks like: warning: Watchman unavailable: "watchman" executable not in PATH (%s), while executing [Errno 2] No such file or directory With the change, it now looks like: warning: Watchman unavailable: "watchman" executable not in PATH ([Errno 2] No such file or directory) Differential Revision: https://phab.mercurial-scm.org/D322