fix the display of selection range that is off-by-one on prompt.

A trivial example to demostrate the error:

	[~/src/CLI-Helpers]
	> perl -Ilib -MCLI::Helpers=:all -e 'prompt("pick one", menu => ["a".."e"])'
	pick one

	    1. a
	    2. b
	    3. c
	    4. d
	    5. e

	Selection (1-6):

                     ^-- wrong