Keep "I" capitalized in str_to_sentence for the "en" locale

[ZIBOWANGKANGYU]

Currently, the single upper-case letter "I" is changed to "i" if it appears in the middle of a sentence.

> stringr::str_to_sentence("THIS IS WHAT I MEAN!")
[1] "This is what i mean!"

It might be a good idea to keep "I" capitalized. Sorry if this discussion is more suitable for the stringi package.

[hadley]

This function is a very thin wrapper around stri_trans_totitle(), so stringi would be the write place to file an issue.