Fix syntax highlighting with "~S" sigil

[feliperenan]

Fixes #438

Just changed to use the same pattern used in elixirString

vim-elixir/syntax/elixir.vim

Line 77 in 34873ee

syn region elixirString matchgroup=elixirStringDelimiter start=+\z('''\)+ end=+^\s*\z1+ contains=@Spell,@elixirStringContained

Before

After

[jbodah]

Thanks, looks great! Would you mind adding a test for this?

Here's an example: https://github.com/elixir-editors/vim-elixir/blob/master/spec/syntax/doc_spec.rb#L27-L36

I'll run those prior on my machine and merge if it all looks good

[feliperenan]

@jbodah Tests added. I'm not sure if they are covering the scenarios correctly though, could you please take a look?

[jbodah]

Looks good - thanks again!