Fix for Turkish "small dotless i" problem in Utf8::toAscii

Currently when you have an "ı" (small dotless i) in your string, Utf8::toAscii doesn't convert properly this character. "ı" converted to "?" instead of "i".

This is a [known Unicode CLDR bug](http://unicode.org/cldr/trac/ticket/2970) opened 3 years ago and does not seem to be fixed. They said "it should be fixed next release, in bug [#3335](http://unicode.org/cldr/trac/ticket/3335)" which opened 2 years ago.
I don't know when they fix that, but that bug causes problem like this one laravel/framework#552