Don't modify constant data in exercise 1.1.3

[leuler]

Not to teach bad habits to the reader, I'd like to suggest to build the example lists in exercise 1.1.3 using LIST instead of QUOTE. Maybe additionally use elements that are self-evaluating to avoid having to write too many quotes, so
(defvar test-list-a (list 1 2 3))
I don't know whether it's didactically better to change the way how test-list-b is constructed, too.

[thephoeron]

Thanks! that's a valid point. I have updated the exercise accordingly.