add julia to lsp-language-id-configuration

[gdkrmr]

There is a very nice Language Server implementation for julia:
https://github.com/JuliaEditorSupport/LanguageServer.jl/

And an Emacs package for this:
https://github.com/non-Jedi/lsp-julia

[codecov]

Codecov Report

Merging #827 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #827   +/-   ##
=======================================
  Coverage   51.51%   51.51%           
=======================================
  Files           5        5           
  Lines          66       66           
=======================================
  Hits           34       34           
  Misses         32       32

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