Auto merge of #255 - est31:master, r=SimonSapin

Switch from rustc-serialize to serde_json

Fixes #253

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/rust-cssparser/255)
<!-- Reviewable:end -->

Author: bors-servo

Cargo.toml

@@ -14,7 +14,7 @@ build = "build.rs"
 exclude = ["src/css-parsing-tests/**", "src/big-data-url.css"]
 
 [dev-dependencies]
-rustc-serialize = "0.3"
+serde_json = "1.0"
 difference = "2.0"
 encoding_rs = "0.8"
 

src/lib.rs

@@ -82,7 +82,7 @@ extern crate encoding_rs;
 #[doc(hidden)]
 pub extern crate phf as _internal__phf;
 #[cfg(test)]
-extern crate rustc_serialize;
+extern crate serde_json;
 #[cfg(feature = "serde")]
 extern crate serde;
 #[cfg(feature = "heapsize")]