* Switch nix grammar repository location to the new repo. The author
has transferred the repository to 'nix-community'.
* Capture ':' and '...' as 'punctuation.delimiter'.
* avoid coloring `identifier`s globally
* fix function application when not part of `select_expression`
* add `has_attribute_expression` highlighting
* fix precendence for interpolation, which should be after select
* highlight `@` as delimiter
