cargo: bump MSRV to 1.67.0

Author: decathorpe

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
 
     strategy:
       matrix:
-        rust: ['stable', 'nightly', '1.59.0']
+        rust: ['stable', 'nightly', '1.67.0']
 
     steps:
       - uses: actions/checkout@v2

Cargo.toml

@@ -5,7 +5,7 @@ license = "MIT OR Apache-2.0"
 
 version = "2.0.2"
 edition = "2021"
-rust-version = "1.59.0"
+rust-version = "1.67.0"
 
 authors = ["Fabio Valentini <decathorpe@gmail.com>"]
 readme = "README.md"