Adding a recipe for julia-mode.

This package adds syntax highlighting for Julia, a programming language
targeting high-performance computing. It's very lispy, influenced by
Common Lisp and Dylan.

Upstream repo is here: https://github.com/JuliaLang/julia

I'm not a Julia core team member, just a fan.
Merge pull request #1920 from Wilfred/julia_mode

Adding a recipe for julia-mode.