message: NOBUG Updated CHANGELOG with the serde change for 0.4.0
diff: @@ -2,6 +2,7 @@ Tantivy 0.4.0
  ==========================
  - Removed u32 fields. They are replaced by u64 and i64 fields (#65)
  +- Replacing rustc_serialize by serde. Kudos to @KodrAus and @lnicola
  - QueryParser:
  - Explicit error returned when searched for a term that is not indexed
  - Searching for a int term via the query parser was broken `(age:1)`
  