Allow "@" character in profile name

Hi,

I love the look of this tool and seems like a much more intuitive way to clone CodeCommit repositories than the previous `!aws codecommit credential-helper $@` method.

However, right now my company can't adopt this tool since we generally always use the `@` character in our profile names (`role_name@account_name`). Is it possible for this to be supported? Whether it be via escaping the `@` with a backslash, or quoting the profile name, or some other design :)

Thanks!
Toby