Update Cargo.toml doc url

Author: alexcrichton

Cargo.toml

@@ -7,7 +7,7 @@ license = "MIT/Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/alexcrichton/stacker"
 homepage = "https://github.com/alexcrichton/stacker"
-documentation = "http://alexcrichton.com/stacker"
+documentation = "https://docs.rs/stacker"
 description = """
 A stack growth library useful when implementing deeply recursive algorithms that
 may accidentally blow the stack.