man: Add missing period to a sentence in dselect(1)

man/dselect.1

@@ -220,7 +220,7 @@ Configures any previously installed, but not fully configured packages.
 Removes or purges installed packages, that are marked for removal.
 .sp
 .SS quit
-Quit \fBdselect\fP
+Quit \fBdselect\fP.
 .sp
 Exits the program with zero (successful) errorcode.
 .sp