Use latest rustc-serialize and increment version for crates.io

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 
 name = "num"
-version = "0.1.23"
+version = "0.1.24"
 authors = ["The Rust Project Developers"]
 license = "MIT/Apache-2.0"
 homepage = "https://github.com/rust-lang/num"
@@ -14,5 +14,5 @@ rational, and complex types.
 """
 
 [dependencies]
-rustc-serialize = "0.3.5"
+rustc-serialize = "0.3.13"
 rand = "0.3.3"