fixup CHANGELOG for v190
fixup CHANGELOG for v190

typo had '7.4.15' instead of '7.4.16' for PHP

Fixes #466

heroku/heroku-buildpack-php,emeth-/heroku-buildpack-php,emeth-/heroku-buildpack-php,emeth-/heroku-buildpack-php,emeth-/heroku-buildpack-php,heroku/heroku-buildpack-php,heroku/heroku-buildpack-php,heroku/heroku-buildpack-php