Fix error for env variables example in docker reference
Fix error for env variables example in docker reference

Signed-off-by: Charles Law <0383b9a5c02b8bc248c0ea9023a23f44780f838f@conduce.com>

thaJeztah/cli,dnephin/cli,allencloud/cli,redpanda/cli,dnephin/cli,docker/cli,allencloud/cli,Zebrilee/cli,ashfall/cli,Zebrilee/cli,riyazdf/cli,docker/cli,e11137/cli,cpuguy83/cli,e11137/cli,cpuguy83/cli,thaJeztah/cli,redpanda/cli,riyazdf/cli,ashfall/cli