Add Vue.js Icon

[mrdrogdrog]

This PR adds the vue.js logo from vuejs/art#12

Fixes #172

[shinenelson]

Please re-base with the head branch.

---

Also, when I built the icon locally, there was a white-space removal change at the end of <path>

- 639.98761,1006.8369 Z" />
+ 639.98761,1006.8369 Z"/>

Do you have the same change?

[mrdrogdrog]

fixed it. (to make things a bit easier for me I rebased this branch on #354)

[shinenelson]

I had this feeling that something was off about this logo when I first built this pull request.

Now when I was looking at the id, it occurred to me that I could check with Font Awesome. Font Awesome has the vuejs logo where the dark and alpha are inverted ( from this pull request ).

It led me to wonder to check again with the actual Vue.js logo on the project website. And then the Font Awesome version made more sense because the darker color in the logo is in the top of the logo and not along the logo. ( Personally, I prefer the Font Awesome representation ).

But considering this version was accepted by the upstream project, I am not sure how it feels about Font Awesome's representation of the brand. Ping @yyx990803 to get feedback on how the Vue.js project feels about this.

[shinenelson]

let us use an id that is requested in the icon request issue, i.e, fa-vue / fa-vuejs. Maybe we could also set up an alias for both.

[mrdrogdrog]

Since the name of the lib is "vue.JS" I chose fa-vuejs.

[shinenelson]

If you would like, you could add an aliases key for the icon in src/icons/icons.yml, but that is not a requirement though.

[shinenelson]

I am going to leave this open for a while to see if we can get direct feedback from the Vue.js project regarding the black and alpha that I raised in my previous review comment ( after comparing with Font Awesome ).