Blog Offensive Terminology Removal

[Marky Jackson]

To follow the terminology [email sent by @slide](https://groups.google.com/d/msg/jenkinsci-dev/CLR55wMZwZ8/uDjgGlnKAQAJ) the Advocacy & Outreach SIG met on 6/11/2020 and one action item was to revisit all previous Jenkins.io blog post and remove offensive terminology where possible. This action item has resulted in the following [PR](https://github.com/jenkins-infra/jenkins.io/pull/3447).

It is worth noting:

• General text with `slave` terminology has been renamed to `agent`
  
• Various references could not be changed due to upstream classes/plugin/reference blogs with terminology
  

There are many places the community is working to remove offensive terminology, we have made many [changes](https://www.jenkins.io/blog/2020/05/06/docker-agent-image-renaming/) and there are still more to go.

Thanks kindly.