The last version that supported node 4 is 1.143.6. You can install it by running npm i -g snyk@1.143.6.
On April 30, 2018, Node.js 4 was officially marked as End of Life (EOL) and ceased to receive security updates.
Snyk highly recommends that you follow a migration path to a stable and officially supported version of Node.js to be able to receive bug and security fixes. Upgrade your version to at least Node.js 10 Dubnium (although Snyk recommends 12 Erbium, the latest LTS).