Added support for Elixir

[akoutmos]

Requirements (please check off with 'x')

• I have read the Contributing Guidelines
• I have read or at least glanced at the FAQ
• I have read or at least glanced at the Wiki

What does this Pull Request (PR) do?

Adds support for Elixir file types

How should this be manually tested?

Open up a .ex, .exs, and .eex file and you should see the Elixir icon

Screenshots (if appropriate or helpful)

[alexparker]

Bump this! Just forked the repo, and merged this into my fork 👍 Need me my elixir icons :)

[akoutmos]

Giving this a friendly bump :)

[HendrikPetertje]

bumpity bump. Would love the nice drops of elixir in my vim

[HendrikPetertje]

Could you be a champ (i can fork your fork ofc, but since this one has taken months to merge...)
aaand

Should .erb (sneaking ruby in here) & .eex perhaps be either one of:
nf-mdi-xml aka:

nf-seti-htmlaka:

?

[kubaugustyn]

Bump :)

[antmachine]

bump 🌮

[ryanoasis]

Sorry for the delay. Thanks @akoutmos