Set version to 3.0.6

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
#
# Date:      Thu Nov 26 09:16:28 2020 -0500
#
# On branch master
# Your branch is up to date with 'origin/master'.
#
# Changes to be committed:
#	modified:   README
#
# Untracked files:
#	demos/pytipc/connection/client.spec
#	demos/pytipc/connection/server.spec
#	demos/pytipc/hello_world/hello_client.spec
#	demos/pytipc/hello_world/hello_server.spec
#	test/rdm/rdm_receiver
#	test/rdm/rdm_sender
#	utils/tipc-trace/tipc-trace
#	utils/tipc-trace/tipc-trace.spec
#
