build: set rust-version=1.63.0

Per discussion on [this urlo
thread](https://users.rust-lang.org/t/best-community-practices-for-msrv/119566),
there is no firm rule on utilization of MSRV. Here, we will opt to
advertise a MSRV that is compatible w/ `reqwest`'s current MSRV, and
compatible with this crate's current dependencies. Note that the
dependency `time` must be `0.3.20` or earlier to satisfy this MSRV; as
MSRV increase is not considered a semver breaking change, we do not
restrict our specification of the `time` dependency to uphold any
guarantee here :(.

Cargo.toml

@@ -4,7 +4,7 @@ description = "Implementation of Cookie storage and retrieval"
 name = "cookie_store"
 version = "0.21.0" # managed by release.sh
 edition = "2021"
-rust-version = "1.67.1"
+rust-version = "1.63.0"
 repository = "https://github.com/pfernie/cookie_store"
 documentation = "https://docs.rs/cookie_store"
 readme = "README.md"