`toc` strips newline from end of file

[RichardBradley]

Traditionally, text files should end with a newline char.

The toc command strips the trailing newline from a README which has one.

I think that toc should either not change the presence or absence of a trailing newline, or if it does want to take an opinion on this issue, it should add one rather than remove one.

(incorrectly raised at jonschlinkert/markdown-toc#35 )