The maven repository appears to be down. Trying to fetch data from the following url results in an error:
https://download.01.org/crosswalk/releases/crosswalk/androi
There is already an open issue in their jira and another one on github. I guess it should be fixed by tomorrow (monday) as none of their maintainers will work on a weekend, be patient.
As the project maintainers stated here there will be no new releases but the source and repos will still be available for development.
Edit:
You can find a workaround until the servers are up again here.