Change Jade to Pug

[MachinisteWeb]

In the file https://github.com/vuejs/vuejs.org/blob/master/src/v2/guide/single-file-components.md

We think (french translate team) which the

As promised, we can also use preprocessors such as Jade, Babel (with ES2015 modules), and Stylus for cleaner and more feature-rich components.

Should be

As promised, we can also use preprocessors such as Pug, Babel (with ES2015 modules), and Stylus for cleaner and more feature-rich components.

If we see others place with Jade term, we notify this here !