It’s a global outage in JCenter. You can monitor status at https://status.gradle.com. It replaces the bintray status page which seems is now fully sunset and returns a 502 error.
UPDATE Jan 13, 06:35 UTC
JCenter is now back online, and systems are fully operational.
UPDATE Jan 20
Gradle Plugin resolution outage postmortem
https://blog.gradle.org/plugins-jcenter
Following this incident, the Gradle Plugin Portal now uses a JCenter mirror hosted by Gradle instead of JCenter directly. This should shield users from short JCenter outages for libraries that have been cached by the mirror. We saw another short outage of JCenter over the weekend and this did not appear to impact Gradle Plugin Portal users.