Update to Rust 2021, MSRV 1.56

Prompted by recent updates in the `time` crate

.github/workflows/test.yml

@@ -28,8 +28,8 @@ jobs:
     strategy:
       fail-fast: false # Even if one job fails we still want to see the other ones
       matrix:
-        # 1.53 is MSRV. Keep this in sync with Cargo.toml
-        rust: [1.53, stable, nightly]
+        # 1.56 is MSRV. Keep this in sync with Cargo.toml
+        rust: [1.56, stable, nightly]
         # NOTE: We don't really have any "feature combos" to test.
         #
         # We just have default features and nothing else :)

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "slog-bunyan"
 version = "2.4.0"
-edition = "2018"
+edition = "2021"
 authors = ["Dawid Ciężarkiewicz <[email protected]>"]
 description = "Bunyan formatter for slog-rs"
 keywords = ["log", "logging", "structured", "hierarchical"]
@@ -17,10 +17,7 @@ readme = "README.md"
 # Changing this bumps the minor version for semver (2.x for semver).
 #
 # NOTE: Changing this requires updating github actions
-#
-# The first version of Cargo that supports this field was in Rust 1.56.0.
-# In older releases, the field will be ignored, and Cargo will display a warning.
-rust-version = "1.53"
+rust-version = "1.56"
 
 [lib]
 path = "lib.rs"