[m-users.] Suggest minor change in 11.3 of the Reference manual

[fabrice nicol]

I just bumped into a little mistake in section 11.3 of the Reference manual:

"For example, the function ‘make_list’ constructs a value of type 
‘list_of_showable’ "

This should be changed into:

"For example, the function ‘make_list’ constructs a value of type 
‘showable_list’ "

(As correctly written in the Mercury code for that matter. It is just a 
redactional issue.).

Fabrice