Add some symbols to punctuation in strip_punctuation

Hi,

Since `"` and `'` are considered punctuation in English, I thought it would be a good idea to add this characters in the function `strip_punctuation!` in the `preprocessing` module. I don't know if there is a reason for not including them in the regex, but I needed them in a project of mine, so here is a patch if you think it could be useful for others too.

Bests,
Remusao