go.mod: bump to Go 1.20

Reviewed-by: Maisem Ali <[email protected]>
Signed-off-by: Jordan Whited <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: jwhited

README.md

@@ -46,7 +46,7 @@ This will run on OpenBSD. It does not yet support sticky sockets. Fwmark is mapp
 
 ## Building
 
-This requires an installation of [go](https://golang.org) ≥ 1.18.
+This requires an installation of the latest version of [Go](https://go.dev/).
 
 ```
 $ git clone https://git.zx2c4.com/wireguard-go

go.mod

@@ -1,6 +1,6 @@
 module golang.zx2c4.com/wireguard
 
-go 1.19
+go 1.20
 
 require (
 	golang.org/x/crypto v0.6.0