Increase Ubuntu target version

Containerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:20.04
+FROM ubuntu:22.04
 
 ENV RUSTUP_HOME=/usr/local/rustup \
     CARGO_HOME=/usr/local/cargo \

README.md

@@ -15,7 +15,7 @@ replacement for dateparser in Rust)
 
 Recommended method.
 
-By default, this builds targeting Ubuntu 20.04. Modify the Containerfile if you wish to target a
+By default, this builds targeting Ubuntu 22.04. Modify the Containerfile if you wish to target a
 different platform. These instructions are written using `podman`, but `docker` should work too.
 
 1. Install container software and Make: `sudo apt install podman make`.