Remove the conditional dependency

[ire4ever1190]

Have been getting this warning in latest devel Nim which leads to the package not getting installed

  Warning:  Declarative parser failed, the file had to be parsed with the VM parser. Please fix your nimble file.
  Warning:  /home/runner/.nimble/pkgs2/lowdb-0.2.1-e26a392547b826d7d3e6566dc0fd76e9f42ead06/lowdb.nimble(9, 2) 'requires' cannot be nested inside control flow statements

Latest Nimble enables the declarative parser by default which is causing lowdb to not be installed correctly since it doesn't like the structure. This removes the conditional and bumps to minimum Nim that db_connector (minimum is 1.7.3 which was a dev version, so made minimum 2.0.0 which was the next stable)

[PhilippMDoerner]

Thanks for the update!