switch jar URL on the JOSM Plugins page back to Gitlab-hosted

As a stop-gap measure to deliver a fix for a bug, I switched the URL of the Rovas Conenctor jar file from https://josm.gitlab.io/plugin/RovasConnector/dist/RovasConnector.jar to the one hosted on the Rovas server. This needs to be reverted back once the automatic build process in this repo works again.

The change was made on the https://josm.openstreetmap.de/wiki/PluginsSource page which in turn is used by the https://josm.openstreetmap.de/wiki/Plugins page to control the JOSM application plugins list.