src: fix typo in #endif comment

PR-URL: https://github.com/nodejs/node/pull/8989
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Brian White <mscdex@mscdex.net>

src/node_os.cc

@@ -16,7 +16,7 @@
 # include <unistd.h>        // gethostname, sysconf
 # include <sys/param.h>     // MAXHOSTNAMELEN on Linux and the BSDs.
 # include <sys/utsname.h>
-#endif  // __MINGW32__
+#endif  // __POSIX__
 
 // Add Windows fallback.
 #ifndef MAXHOSTNAMELEN