Update aws-ec2.md (#2096)
Update aws-ec2.md (#2096)

The https://www.spinnaker.io/downloads/aws/managing.yaml URL gives a 301 to https://spinnaker.io/downloads/aws/managing.yaml. Unfortunately, with the way the instructions are written, rather than following the redirect, `curl -O` will just save the 301 result to the yaml file. I have updated the URLs so the redirect does not happen and added the -L flag just in case this happens again (instructs curl to follow redirects rather than return them)

Co-authored-by: Dave Dorbin <3a983b921291999521a653180c5b82ccd2c36700@google.com>
spinnaker/spinnaker.github.io,spinnaker/spinnaker.github.io,spinnaker/spinnaker.github.io