Downgrade to tree-sitter 0.20.0

0.20.1 has a performance regression, which seems to particularly
affect Elixir parsing:
https://github.com/tree-sitter/tree-sitter/issues/1510

CHANGELOG.md

@@ -5,6 +5,8 @@
 Moved to the [official Elixir
 parser](https://github.com/elixir-lang/tree-sitter-elixir).
 
+Fixed a parsing performance regression introduced in 0.13.
+
 ## 0.14 (released 27 December 2021)
 
 ### Parsing

Cargo.lock

@@ -455,9 +455,9 @@ dependencies = [
 
 [[package]]
 name = "tree-sitter"
-version = "0.20.1"
+version = "0.20.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9394e9dbfe967b5f3d6ab79e302e78b5fb7b530c368d634ff3b8d67ede138bf1"
+checksum = "63ec02a07a782abef91279b72fe8fd2bee4c168a22112cedec5d3b0d49b9e4f9"
 dependencies = [
  "cc",
  "regex",

Cargo.toml

@@ -31,7 +31,7 @@ rustc-hash = "1.1.0"
 strsim = "0.10.0"
 lazy_static = "1.4.0"
 atty = "0.2.14"
-tree-sitter = "0.20.1"
+tree-sitter = "=0.20.0"
 libc = "0.2.108"
 log = "0.4.14"
 pretty_env_logger = "0.4.0"