Default value for profile argument should be the default profile

[mantoine96]

In the list of arguments in the README.md for okta-aws-cli it is written:

Name	Description	Command line flag	ENV var and .env file value
Profile	Default is default	--profile [value]	OKTA_AWSCLI_PROFILE

However, when using okta-aws-cli v2.1.2, this is the result you get when nothing is specified, despite a default profile being present:

$ okta-aws-cli web
Error: missing flags:
  --org-domain
  --oidc-client-id

This PR therefore sets the default value for the profile to be default as described in the documentation.

[monde]

Thanks @mantoine96 this will go out in the next release.