Fix the 1.12.8 release announcement

As suggested by @ramsey [here](http://framework.zend.com/blog/zend-framework-1-12-8-released.html#comment-1572198749), I added the PR [zf1#418](https://github.com/zendframework/zf1/pull/418) to the Notable Changes section. Moreover, I added a new section: Potential BC break, to show how to fix SQL code using the `Zend_Db_Expr` function.