Fix/custom types select queries

[marksto]

@camsaul Addresses the issue #88.

• [x] Ensure the PR follows the Clojure Style Guide and the Metabase Clojure Style Guide.
• [x] Tests and linters pass. You can run them locally as follows: lein test && lein lint
• [x] Make sure you've included new tests for any new features or bugfixes
• [x] New features are documented, or documentation is updated appropriately for any changed features. [regression issue]
• [x] Carefully review your own changes and revert any superfluous ones.
• [x] Include a detailed explanation of what changes you're making and why you've made them. [see the issue for details]