Fix lintian warning: macro 'RG' not defined

doc/man1/rigctl.1

@@ -27,7 +27,7 @@ rigctl \- control radio transceivers and receivers
 .OP \-c id
 .OP \-t char
 .OP \-C parm=val
-.RG \-Y
+.RB \-Y
 .RB [ \-v [ \-Z ]]
 .RB [ command | \- ]
 .YS