Your curl command is entirely wrong. You should be using the following

curl -H 'Authorization: token <MYTOKEN>' ...

That aside, that doesn’t authorize your computer to clone the repository if in fact it is private. (Taking a look, however, indicates that it is not.) What you would normally do is the following:

git clone https://scuzzlebuzzle:<MYTOKEN> --branch=gh-pages gh-pages

That will add your credentials to the remote created when cloning the repository. Unfortunately, however, you have no control over how Travis clones your repository, so you have to edit the remote like so.

# After cloning
cd gh-pages
git remote set-url origin https://scuzzlebuzzle:<MYTOKEN>

That will fix your project to use a remote with credentials built in.

Warning: Tokens have read/write access and should be treated like passwords. If you enter your token into the clone URL when cloning or adding a remote, Git writes it to your .git/config file in plain text, which is a security risk.