Fix Predicate spec for wildcard escaping

This fix reflects commit 71a3938a1c9c4d593b59ac7a0c6296439cd471ad.
Update Ransack::Constants#escape_wildcards

This updates Ransack::Constants#escape_wildcards to escape dots (.) as
well in order to bypass rails/rails#950.
Merge pull request #191 from KevinSjoberg/master

Update Ransack::Constants#escape_wildcards