add ilike operator

[sylvainlap]

Allows to support the postgres ILIKE operator.

[daffl]

Thank you! Is there any other operators you think we should map? New operators also need to be added to the documentation at https://docs.feathersjs.com/api/databases/knexjs.html#querying.

[sylvainlap]

the documentation has been updated here: feathersjs/docs#886

[daffl]

Sweet, thank you. A test would be nice as well. Probably just a copy of https://github.com/feathersjs-ecosystem/feathers-knex/blob/master/test/index.test.js#L106 querying for %char%

[sylvainlap]

I cannot add a test, because your tests run sqlite, and ilike is a psql only operator.

[daffl]

Makes sense. I created a follow-up issue in #128 to run CI against other dbs as well so we can revisit this then.