Fix LGTM Erros & Warnings and Recomandations

[matbrgz]

1 alert of Incomplete string escaping or encoding in precommit.js
3 alerts of Useless assignment to local variable in image.js
1 alert of Unused variable, import, function or class in index.js

https://lgtm.com/projects/g/dadi/cdn/alerts/

[eduardoboucas]

Hi @MatheusRV, thanks for bringing this tool to our attention. We'll look into the issues flagged. Since they're small optimisations, we'll roll them out in future releases.

We'll keep this issue open until we sort them.

Thanks!