Update Cargo.toml doc url

Cargo.toml

diff --git a/Cargo.toml b/Cargo.toml
index 91da30c..6dc5077 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,7 +6,7 @@
 readme = "README.md"
 repository = "https://github.com/alexcrichton/rustc-demangle"
 homepage = "https://github.com/alexcrichton/rustc-demangle"
-documentation = "http://alexcrichton.com/rustc-demangle"
+documentation = "https://docs.rs/rustc-demangle"
 description = """
 Rust compiler symbol demangling.
 """