Fix URL in install.sh script when installing with curl

- when currently running `curl https://npmjs.org/install.sh` it returns:

        <html>Moved: <a href="https://www.npmjs.org/install.sh">https://www.npmjs.org/install.sh</a>

This causes the install script to exit with `Syntax error: newline unexpected`.

I'm not sure if the redirect was made on purpose, anyway it breaks the
installation process.