Changing `nth` to `n'th` doesn't strike me as right; `nth` is how I at least am used to seeing it. c.f. [ngrams comparison of `nth`, `n'th` and `n-th`](http://books.google.com/ngrams/graph?content=nth%2Cn%27th%2Cn-th&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=), where `nth` has an overwhelming victory.