doc: Update Ryu Ishimoto's IRC nick
doc: Update Ryu Ishimoto's IRC nick

It seems he prefers this nick these days.

Change-Id: I726448149fa534cde717278bb42a2108dcd3742e

cloudbase/neutron,igor-toga/local-snat,mahak/neutron,klmitch/neutron,huntxu/neutron,igor-toga/local-snat,wolverineav/neutron,huntxu/neutron,noironetworks/neutron,bigswitch/neutron,mahak/neutron,openstack/neutron,dims/neutron,bigswitch/neutron,MaximNevrov/neutron,klmitch/neutron,dims/neutron,mahak/neutron,sebrandon1/neutron,sebrandon1/neutron,cloudbase/neutron,eayunstack/neutron,wolverineav/neutron,noironetworks/neutron,eayunstack/neutron,openstack/neutron,MaximNevrov/neutron,openstack/neutron