Update usage line

bin/mkexec

@@ -97,7 +97,7 @@ if (exists $bangs->{$type}) {
 ## '''' ##   ..............................................................-'
 
 sub usage {
-    print STDERR "usage: $0 [-f|-E] filename [type] [purpose]\n";
+    print STDERR "usage: $0 [-f|-e] filename [type] [purpose]\n";
     exit 0;
 }