Updated CHANGELOG with description of ruby-grape#208

Author: Pedro Padron

CHANGELOG.markdown

@@ -6,6 +6,7 @@ Next Release
 * [#181](https://github.com/intridea/grape/pull/181): Fix: Corrected JSON serialization of nested hashes containing `Grape::Entity` instances - [@benrosenblum](https://github.com/benrosenblum).
 * [#203](https://github.com/intridea/grape/pull/203): Added a check to `Entity#serializable_hash` that verifies an entity exists on an object - [@adamgotterer](https://github.com/adamgotterer).
 * [#204](https://github.com/intridea/grape/pull/204): Added ability to declare shared parameters at namespace level - [@tim-vandecasteele](https://github.com/tim-vandecasteele).
+* [#208](https://github.com/intridea/grape/pull/208): `Entity#serializable_hash` must also check if attribute is generated by a user supplied block - [@ppadron][https://github.com/ppadron].
 
 0.2.1 (7/11/2012)
 =================