use ink! 4.0.0-beta for example contract

Author: achimcc

Cargo.lock

@@ -1,12 +1,12 @@
 [package]
 name = "contract"
-version = "4.0.0-alpha.3"
+version = "4.0.0-beta"
 authors = ["Parity Technologies <[email protected]>"]
 edition = "2021"
 publish = false
 
 [dependencies]
-ink = { version = "4.0.0-alpha.3", default-features = false }
+ink = { version = "4.0.0-beta", default-features = false }
 
 scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
 scale-info = { version = "2", default-features = false, features = ["derive"], optional = true }