Exclude buck2 prelude submodule from published crate

Author: dtolnay

Cargo.toml

@@ -6,7 +6,7 @@ categories = ["development-tools::ffi", "api-bindings", "no-std"]
 description = "Safe interop between Rust and C++"
 documentation = "https://docs.rs/cxx"
 edition = "2018"
-exclude = ["/demo", "/gen", "/syntax", "/third-party"]
+exclude = ["/demo", "/gen", "/syntax", "/third-party", "/tools/buck/prelude"]
 homepage = "https://cxx.rs"
 keywords = ["ffi", "c++"]
 license = "MIT OR Apache-2.0"