Exercise 7.1 references nonexistent Exercise 6.6

[mz0]

ex7_1.md:127 "The solution will look almost the same as for Exercise 6.6"
though there's no Exercise 6.6 in sight.

python-mastery/Exercises/ex7_1.md

Line 127 in bc3b595

fiddly bits. The solution will look almost the same as for Exercise 6.6. Don't

[dabeaz]

Changed to reference 6.5