man: Update u-a log file reference

update-alternatives has now its independent log file, reflect that in
the man page.

man/update-alternatives.8

@@ -333,7 +333,7 @@ different from the default.
 .TP
 .BI \-\-log " file"
 Specifies the log file, when this is to be different from the default
-(/var/log/dpkg.log).
+(/var/log/alternatives.log).
 .TP
 .BI \-\-force
 Let \fBupdate-alternatives\fR replace any real file that is installed