Update Ransack::Constants#escape_wildcards

This pull requests bypasses rails/rails#950. When a string such as  `foo.bar` is used in an ActiveRecord query it is misinterpreted due to eager loading functionality and produces an awfully verbose query. This bypasses this by escaping dots (.) in `LIKE` patterns.

This pull request also reflects commit 71a3938a1c9c4d593b59ac7a0c6296439cd471ad by updating the Predicate spec.

I ran all tests before opening this pull request and can confirm that they all pass.