Update Knex config to avoid hanging promises

When trying to work with the DB in the tests we were getting

```
Jest did not exit one second after the test run has completed.

This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.
```

Googling led us to [Having trouble running Jest, unhandled Promises](Vincit/objection.js#1015) and [Need to explicit destroy knex in order to stop the script](Vincit/objection.js#534). The second issue included a comment that setting the pool min size to 0 and idleTimeoutMillis to 500 would solve the problem. We tried it and it worked!

knexfile.js

@@ -30,6 +30,7 @@ const development = {
 
 const test = {
   ...defaultConfig,
+  pool: { min: 0, idleTimeoutMillis: 500 },
   connection: {
     ...defaultConnection,
     database: DatabaseConfig.testDatabase