Bump parking-lot to version 0.12.0

Summary:
~~~Added new parking-lot version named parking_lot_0_12~~~
allow-large-files

previous versions of parking-lot are incompatible with wasm compilation targets

rustwasm/wasm-bindgen#2160
Amanieu/parking_lot#302

Reviewed By: dtolnay

Differential Revision: D33985872

fbshipit-source-id: ce571ef50289fe97ff89dbf72d2c7f39fbd47758

shed/lock_ext/Cargo.toml

@@ -11,4 +11,4 @@ repository = "https://github.com/facebookexperimental/rust-shed/"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
-parking_lot = { version = "0.11.2", features = ["send_guard"] }
+parking_lot = { version = "0.12.0", features = ["send_guard"] }