Fix Iglu Server's swagger ui

[istreeter]

Iglu server has a swagger ui, which should be available under /iglu-server/static/swagger-ui/index.html. But for Mini the page gives this error message:

Fetch error undefined /api/schemas/swagger.json

The Iglu Server hocon documentation says it takes a paramter swagger.baseUrl which we are not setting for Mini. I haven't checked yet, but I wonder if this is the reason for the error.

[istreeter]

This will be partly fixed by #341 , which includes Iglu-server fix snowplow/iglu-server#89. But we also need to update the swagger.baseUrl param in the hocon.