[Elixir] Update syntax

[hkrutzer]

• My commit messages start with the package name in square brackets, e.g. [XML].
• I have included new or enhanced syntax tests to cover the changes.
• I have included a performance comparison below:

Performance

Before changes

Syntax "Packages/PackageName/lang.sublime-syntax" took an average of 10.0ms over 10 runs
Syntax "Packages/PackageName/lang-types.sublime-syntax" took an average of 2.0ms over 10 runs

After changes

Syntax "Packages/PackageName/lang.sublime-syntax" took an average of 10.2ms over 10 runs
Syntax "Packages/PackageName/lang-types.sublime-syntax" took an average of 2.0ms over 10 runs

[slimsag]

Thanks for doing this! I'll merge this now, and it will go live on Sourcegraph.com later today and in the next version of Sourcegraph on Aug 20th (v3.31)

[slimsag]

Ah, unfortunately I've had to back this change out - I just realized the updated syntax uses Sublime Text 4 features (sublime-syntax v2) which the Rust syntax highlighter, Syntect, doesn't support yet: trishume/syntect#323