update manifest.json image path
update manifest.json image path

blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-portal