Remove gulp-util dependency, which is deprecated

[ghost]

Summary

The software still uses gulp-util dependency, which is deprecated.

Currently there is no way to update the dependency, as it is currently blocked by gifsicle-bin, which itself hasn't yet been updated to reflect the changes. Until then, the library will stay.

When, however, the gifsicle library is updated to reflect the change, build should pass and updating to gulp 4.0.0 as well as removing gulp-util dependency should be possible.

More information: https://medium.com/gulpjs/gulp-util-ca3b1f9f9ac5

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[syuilo]

Thanks reporting 🙏

[Johann150]

Fixed in d18291cf0c70757147d5307cdbc8bd70b1e4bbe2.