new icon: pug (original, plain, line) #2174

[GCHQDeveloper926]

• PR does not match another non-stale PR currently opened
• PR name matches the format new icon: Icon name (versions separated by comma). More details here
• PR's base is the develop branch.
• Your icons are inside a folder as seen here
• SVG matches the standards laid out here
• A new object is added in the devicon.json file at the correct alphabetic position as seen here

**This PR closes #567 **

I had a bit of an accident with my git history so opening a new fresh PR.

Link to prove your SVG is correct and up-to-date.

(https://github.com/pugjs/pug-logo/blob/master/SVG/pug-final-logo-_-colour-128.svg)