Update allocator-api2 to v0.3 (#271)

Author: raviqqe

Cargo.toml

@@ -40,7 +40,7 @@ harness = false
 # This dependency provides a version of the unstable nightly Rust `Allocator`
 # trait on stable Rust. Enabling this feature means that `bumpalo` will
 # implement its `Allocator` trait.
-allocator-api2 = { version = "0.2.8", default-features = false, optional = true }
+allocator-api2 = { version = "0.3.0", default-features = false, optional = true }
 
 # This dependency is here to allow integration with Serde, if the `serde` feature is enabled
 serde = { version = "1.0.171", optional = true }