msrv: bump to Rust 1.41.1

This was long overdue, and we were motivated by memchr's move to Rust
2018 in BurntSushi/memchr#82.

Rust 1.41.1 was selected because it's the current version of Rust in
Debian Stable. It also feels old enough to assure wide support.

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
         include:
         - build: pinned
           os: ubuntu-18.04
-          rust: 1.28.0
+          rust: 1.41.1
         - build: stable
           os: ubuntu-18.04
           rust: stable

README.md

@@ -222,7 +222,7 @@ The full set of features one can disable are
 
 ### Minimum Rust version policy
 
-This crate's minimum supported `rustc` version is `1.28.0`.
+This crate's minimum supported `rustc` version is `1.41.1`.
 
 The current **tentative** policy is that the minimum Rust version required
 to use this crate can be increased in minor version updates. For example, if