Update "URL" to domain in connectdlg.cpp

https://github.com/jamulussoftware/jamulus/blob/e375329d6eff0c89a34c121de06d12dbe6b3b5af/src/connectdlg.cpp#L87

shows a wrong text as mentioned by @pljones this should be edited (after this release) a PR can already be raised now.
See below what it should be updated to.