increase MSRV to 1.57 to match http crate

Author: syphar

Cargo.toml

@@ -10,7 +10,7 @@ authors = ["Sean McArthur <sean@seanmonstar.com>"]
 keywords = ["http", "headers", "hyper", "hyperium"]
 categories = ["web-programming"]
 edition = "2018"
-rust-version = "1.56"
+rust-version = "1.57"
 
 [workspace]
 members = ["headers-core"]

headers-core/Cargo.toml

@@ -9,7 +9,7 @@ repository = "https://github.com/hyperium/headers"
 authors = ["Sean McArthur <sean@seanmonstar.com>"]
 keywords = ["http", "headers", "hyper", "hyperium"]
 edition = "2018"
-rust-version = "1.49"
+rust-version = "1.57"
 
 [dependencies]
 http = "1.0.0"