Prepping release of alpha.6 (#5629)

* bumping version

* cargo update

* adding changelog

substrate/utils/build-script-utils/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "substrate-build-script-utils"
-version = "2.0.0-alpha.5"
+version = "2.0.0-alpha.6"
 authors = ["Parity Technologies <admin@parity.io>"]
 edition = "2018"
 license = "GPL-3.0"
@@ -8,8 +8,8 @@ homepage = "https://substrate.dev"
 repository = "https://github.com/paritytech/substrate/"
 description = "Crate with utility functions for `build.rs` scripts."
 
-[dependencies]
-platforms = "0.2.1"
-
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+platforms = "0.2.1"