Rename krate in json to crate

This was changed when switching from rustc serialize to serde; ember
expects the key in the JSON to be "crate" but Rust needs the field in
the struct to be named "krate". The tests didn't catch this because we
aren't testing the serialized JSON string at all; a round trip through
JSON totally worked :-/

Author: carols10cents

src/version.rs

@@ -51,6 +51,7 @@ pub struct NewVersion {
 #[derive(Serialize, Deserialize, Debug)]
 pub struct EncodableVersion {
     pub id: i32,
+    #[serde(rename = "crate")]
     pub krate: String,
     pub num: String,
     pub dl_path: String,