Bump bitvec dependency to 0.22.3

There was a conflict between bitvec and a dependency of it (funty) that
caused a build failure. See:
- ferrilab/bitvec#105
- ferrilab/funty#3

Due to semver, when importing parity-scale-codec as a library and
resolving bitvec 0.20.1 dependencies, funty 0.12 is pulled, which causes
the aforementioned build failure.  I believe this is not happening when
testing parity-scale-codec itself because Cargo.lock pins funty to
1.1.0, but when importing parity-scale-codec from another crate, this
pinning is sometimes not possible.  Bumping bitvec to 0.22.3 solves this
issue, as it is compatible with funty 0.12.

Cargo.toml

@@ -12,7 +12,7 @@ edition = "2018"
 arrayvec = { version = "0.7", default-features = false }
 serde = { version = "1.0.102", optional = true }
 parity-scale-codec-derive = { path = "derive", version = "2.3.1", default-features = false, optional = true }
-bitvec = { version = "0.20.1", default-features = false, features = ["alloc"], optional = true }
+bitvec = { version = "0.22.3", default-features = false, features = ["alloc"], optional = true }
 byte-slice-cast = { version = "1.0.0", default-features = false }
 generic-array = { version = "0.14.4", optional = true }
 arbitrary = { version = "1.0.1", features = ["derive"], optional = true }