hedgewars-engine (rust): fix "protocol_version" -> "hedgewars_engine_protocol_version"
That function/symbol was renamed in ef2fc0210362
[package]
name = "vec2d"
version = "0.1.0"
authors = ["Andrey Korotaev <a.korotaev@hedgewars.org>"]
edition = "2018"
[dependencies]
integral-geometry = { path = "../integral-geometry" }