Problem: no relicense agreement by ssbl

Solution: add it

RELICENSE/ssbl.md

+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Shubham Lagwankar that grants permission to
+relicense its copyrights in the libzmq C++ library (ZeroMQ) under the
+Mozilla Public License v2 (MPLv2) or any other Open Source Initiative
+approved license chosen by the current ZeroMQ BDFL (Benevolent
+Dictator for Life).
+
+A portion of the commits made by the Github handle "ssbl", with
+commit author "Shubham Lagwankar <shubhu105@gmail.com>", are
+copyright of Shubham Lagwankar.  This document hereby grants the libzmq
+project team to relicense libzmq, including all past, present and
+future contributions of the author listed above.
+
+Shubham Lagwankar
+2018/10/30
+