launchd: fix permissions on the plist file

Don't rely on the user have the same umask as me, force the permissions
to be correct.

I'm guessing that the ownership is something that gets fixed on reboot,
which would explain why things start working for folks that reboot.

Refs #90

main.c

@@ -250,6 +250,8 @@ static void spawn_via_launchd(void)
 "</plist>\n",
     watchman_path, log_name, sock_name, watchman_state_file, sock_name);
   fclose(fp);
+  // Don't rely on umask, ensure we have the correct perms
+  chmod(watchman_path, 0644);
 
   append_argv(argv, plist_path);