FIX: Optional :connection-test-query for jtds

Resolves issue where jtds does not support JDBC4 isValid

Also FWIW we use sqlserver and sqlserver-jtds at Outpace, so these could be marked as tested in the README.

AFAIK `:connection-test-query` should be optional key: `(s/optional-key :connection-test-query)`, otherwise test fail with  `Exception in thread "main" java.lang.IllegalArgumentException: Invalid configuration options: (:connection-test-query), compiling:(core_test.clj:23:3)` (I should configure topic branches on CircleCI, no idea why it doesn't work...)

Plus, could you align keys and values of the map in columns?