Update to 0.2.0-alpha.6

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "rustsbi"
 description = "Minimal RISC-V's SBI implementation library in Rust"
-version = "0.2.0-alpha.5"
+version = "0.2.0-alpha.6"
 authors = ["luojia65 <me@luojia.cc>"]
 repository = "https://github.com/rustsbi/rustsbi"
 documentation = "https://docs.rs/rustsbi"