tree-sitter 0.21.0+ compatibility

[HerringtonDarkholme]

Hi I'm ast-grep's author. ast-grep is an AST based search tool that supports elixir.

at the moment tree-sitter-elixir cannot be used with tree-sitter-0.21.0.

More specifically, the cargo manifest disables the usage of newer tree-sitter.

https://github.com/elixir-lang/tree-sitter-elixir/blob/main/Cargo.toml#L23

Appreciate it if you can bump the version dependency!

Reference:
https://github.com/tree-sitter/tree-sitter-go/pull/138/files
https://github.com/tree-sitter/tree-sitter/releases

[jonatanklosko]

I updated to tree-sitter = ">=0.21.0" and released v0.2.0, let me know if there are any issues :)