Check if you don't have a VPN or something like this messing with your connection. Also, check Jenkins DNS configurations (try to start it with "--dns 188.8.131.52".
You have a different solution? A short tip here would help you and many other users who saw this issue last week.
- java.net.UnknownHostException: www.google.co.in at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)