Update Cargo.toml

Author: tkf2019

os/Cargo.toml

@@ -10,4 +10,4 @@ edition = "2021"
 buddy_system_allocator = "0.6"
 lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
 log = "0.4"
-riscv = { git = "https://gitee.com/rcore-os/riscv", features = ["inline-asm"] }
+riscv = { git = "https://github.com/rcore-os/riscv", features = ["inline-asm"] }