docs: update to v0.3.0 reana-client cli
docs: update to v0.3.0 reana-client cli

Signed-off-by: Dinos Kousidis <2232407337c30afa275b4ef42b0b26111a2f9dfc@cern.ch>

reanahub/reana-demo-worldpopulation,tiborsimko/reana-demo-worldpopulation