Prepping release of alpha.6 (#5629)

* bumping version

* cargo update

* adding changelog

substrate/primitives/panic-handler/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "sp-panic-handler"
-version = "2.0.0-alpha.5"
+version = "2.0.0-alpha.6"
 authors = ["Parity Technologies <admin@parity.io>"]
 edition = "2018"
 license = "GPL-3.0"
@@ -9,9 +9,9 @@ repository = "https://github.com/paritytech/substrate/"
 description = "Custom panic hook with bug report link"
 documentation = "https://docs.rs/sp-panic-handler"
 
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
 [dependencies]
 backtrace = "0.3.38"
 log = "0.4.8"
-
-[package.metadata.docs.rs]
-targets = ["x86_64-unknown-linux-gnu"]