fixed a typo in changelog

Signed-off-by: Amir Saboury <amir.saboury@gmail.com>
Merge pull request #3251 from amir-s/develop

fixed a typo in changelog
[ci skip] Remove references to 'PHP5' from comments
Revert #3194

This has caused way too many BC breaks (#3238, #3242, #3257).
Close #3257
Merge branch 'develop' of git://github.com/EllisLab/CodeIgniter into develop