not and greaterThan should work in case insensitive manner

[dmarcelino]

In balderdashy/waterline-adapter-tests#53 I've added case insensitive not and greaterThan tests but unfortunately sails-postgresql is breaking those tests: https://travis-ci.org/balderdashy/waterline-adapter-tests/jobs/59856880#L273

We need to fix this to put sails-postgresql on par with the other adapters.

[dmarcelino]

Waterline-sequel 0.3.1 fixed this (balderdashy/waterline-sequel#41): https://travis-ci.org/balderdashy/waterline-adapter-tests/jobs/60510427#L1796