Error - starting container process caused "exec: \"-k\"

I am following the steps mentioned in the below link to setup in Windows 10 machine:

When trying to run the command :
$ docker run -it --rm webpagetest-api -k YOURAPIKEY test

**I have used the correct API Key in the command above.

I am getting the following error:
docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused “exec: “-k”: executable file not found in $PATH”: unknown.

Please help!