logname: list David MacKenzie as the author

* src/logname.c (AUTHORS): List David as the author.
* AUTHORS: Likewise.

AUTHORS

@@ -44,7 +44,7 @@ join: Mike Haertel
 kill: Paul Eggert
 link: Michael Stone
 ln: Mike Parker, David MacKenzie
-logname: FIXME: unknown
+logname: David MacKenzie
 ls: Richard M. Stallman, David MacKenzie
 md5sum: Ulrich Drepper, Scott Miller, David Madore
 mkdir: David MacKenzie

src/logname.c

@@ -25,7 +25,7 @@
 /* The official name of this program (e.g., no 'g' prefix).  */
 #define PROGRAM_NAME "logname"
 
-#define AUTHORS proper_name ("FIXME: unknown")
+#define AUTHORS proper_name ("David MacKenzie")
 
 void
 usage (int status)