allow URL-unsafe characters inside raw JDBC connection-uri

`ragtime.core/connection` tries to parse the raw-connection-string as a URI which fails if the string contains unsafe characters like `%`. 
Our password contained such characters which lead to `java.net.URISyntaxException: Malformed escape pair ...` when trying to run `lein ragtime migrate`.
Not sure if proposed fix is a hack, otherwise unsafe characters would have to be percent-encoded inside the project.clj/profiles.clj and parsed inside ragtime, which only adds confusion IMHO.

Cheers!