Upgrade to Hugo v0.76.5

It's time for us to look at supporting the latest release of Hugo: https://github.com/gohugoio/hugo/releases/download/v0.76.5/hugo_0.76.5_Linux-64bit.deb

Let's test and make sure this upgrade won't cause any regressions with our websites.

Checklist for upgrading:

For this checklist, I am going to use iot.eclipse.org as an example:

• Update Hugo URL in https://github.com/EclipseFdn/iot.eclipse.org/blob/master/.travis.yml
• Update Hugo version in https://github.com/EclipseFdn/iot.eclipse.org/blob/master/Dockerfile
• Update Hugo version in https://github.com/EclipseFdn/iot.eclipse.org/blob/master/netlify.toml
• Update Hugo version in https://github.com/EclipseFdn/iot.eclipse.org/blob/master/Jenkinsfile