create-amis: use jq instead of json

nixos/maintainers/scripts/ec2/create-amis.sh

···
                     ami=$(aws ec2 copy-image \
                         --region "$region" \
                         --source-region "$prevRegion" --source-image-id "$prevAmi" \
-                        --name "$name" --description "$description" | json -q .ImageId)
+                        --name "$name" --description "$description" | jq -r '.ImageId')
                     if [ "$ami" = null ]; then break; fi
                 else