Update to latest nightly

Fix issue with parking_lot compilation by removing
the dependency on the "nightly" feature...

Author: Techcable

libs/context/Cargo.toml

@@ -12,7 +12,7 @@ edition = "2018"
 zerogc = { path = "../..", version = "0.2.0-alpha.1" }
 once_cell = { version = "1.5", optional = true }
 # Concurrency
-parking_lot = { version = "0.11", features = ["nightly"], optional = true }
+parking_lot = { version = "0.11", optional = true }
 crossbeam-utils = { version = "0.8", optional = true }
 # Logging
 slog = "2.7"

libs/context/src/lib.rs

@@ -2,6 +2,7 @@
     negative_impls, // !Send is much cleaner than `PhantomData<Rc>`
     untagged_unions, // I want to avoid ManuallyDrop in unions
     const_fn, // Apparently this feature is unstable???
+    const_fn_trait_bound, // So generics + const fn are unstable, huh?
 )]
 #![cfg_attr(not(feature = "std"), no_std)]
 //! The implementation of [::zerogc::CollectorContext] that is

libs/simple/Cargo.toml

@@ -14,7 +14,7 @@ once_cell = { version = "1.5", optional = true }
 # Shared impl
 zerogc-context = { path = "../context", version = "0.2.0-alpha.1", default-features = false }
 # Concurrency
-parking_lot = { version = "0.11", features = ["nightly"], optional = true }
+parking_lot = { version = "0.11", optional = true }
 # Logging
 slog = "2.7"