spin 2.0.0 came out

[seungjin]

Fermyon people released Spin 2.0.0.
https://www.fermyon.com/blog/introducing-spin-v2

To use libsql/turso in Fermyon/Spin, spin version in Cargo.toml need to upgrade.

[seungjin]

PR: #57

Seems this spin 2.0 bump-up is duplicated: #49 (comment)