Update bootstrap seeds

Summary: As per title. We update them once in a while to make sure new client start with a seed list that is as up to date as possible.

Test Plan:

make check

Bootstrap a node on test and mainet.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1232