Specify resolver = "2" in the workspace Cargo.toml (#130)

Fixes the below warning:

> warning: virtual workspace defaulting to `resolver = "1"` despite one
or more workspace members being on edition 2021 which implies `resolver
= "2"`
> note: to keep the current resolver, specify `workspace.resolver = "1"`
in the workspace root's manifest
> note: to use the edition 2021 resolver, specify `workspace.resolver =
"2"` in the workspace root's manifest

Author: fornwall

Cargo.toml

@@ -1,2 +1,3 @@
 [workspace]
+resolver = "2"
 members = ["crates/*"]