docs: use correct separator in --security-opt
docs: use correct separator in --security-opt

> Security options with `:` as a separator are deprecated and will be completely unsupported in 17.04, use `=` instead.

Signed-off-by: Felix Geyer <3a9f5f71814a4c500551214ddb4a569b9211e1da@fobos.de>

docker/cli,thaJeztah/cli,thaJeztah/cli,docker/cli