Clean npm dependencies

[laemtl]

First, thanks for this amazing library!
We are using differenceequationsignal1d in our LORIS EEG visualization component and have recently dealing with more than 40 security alerts for vulnerabilities introduced by outdated dependencies from differenceequationsignal1d.

differenceequationsignal1d declares an old version of npm-check-updates as a dependency which requires more than 30 other dependencies that causes those issues. I propose to remove the dependency since npm-check-updates is a tool that can be installed and run globally.