A couple of typo fixes (and github-ery practice)

Hi Ricardo,

Two fixes for [possible] typos in the Sub::Exporter docs.

1. almost certainly an incorrect example (should use 50 passes)
1. a possible typo, import -> importer.

Also practicing github-ery.  I forked your repo, cloned it, made a branch on my machine, committed the fixes, pushed the branch back to my fork on github and then made this pull request with respect to the typos branch.  Please let me know how this worked out for you.

g.