Change --mapfile to --map-file in tftpd(8)

... as the option is called --map-file.

tftp-doc.patch

@@ -25,3 +25,21 @@
  Specify the use of filename remapping.  The
  .I remap-file
  is a file containing the remapping rules.  See the section on filename
+@@ -243,7 +243,7 @@ option, but crash with an error if they
+ accepted by the server.
+ .SH "FILENAME REMAPPING"
+ The
+-.B \-\-mapfile
++.B \-\-map\-file
+ option specifies a file which contains filename remapping rules.  Each
+ non-comment line (comments begin with hash marks,
+ .BR # )
+@@ -395,7 +395,7 @@ flag is used to set up a chroot() enviro
+ once a connection has been set up.
+ .PP
+ Finally, the filename remapping
+-.RB ( \-\-mapfile
++.RB ( \-\-map\-file
+ flag) support can be used to provide a limited amount of additional
+ access control.
+ .SH "CONFORMING TO"