docs: add changelog for 5.0.4

CHANGELOG.md

+<a name="5.0.4"></a>
+## [5.0.4](https://github.com/angular/angular/compare/5.0.3...5.0.4) (2017-12-01)
+
+
+### Bug Fixes
+
+* **animations:** ensure multi-level enter animations work ([#19455](https://github.com/angular/angular/issues/19455)) ([22bbd6e](https://github.com/angular/angular/commit/22bbd6e))
+* **animations:** ensure multi-level leave animations work ([#19455](https://github.com/angular/angular/issues/19455)) ([c7b211c](https://github.com/angular/angular/commit/c7b211c))
+* **common:** accept falsy values as HTTP bodies ([#19958](https://github.com/angular/angular/issues/19958)) ([66fd1f8](https://github.com/angular/angular/commit/66fd1f8)), closes [#19825](https://github.com/angular/angular/issues/19825) [#19195](https://github.com/angular/angular/issues/19195)
+* **common:** don't strip XSSI prefix for if error isn't JSON ([#19958](https://github.com/angular/angular/issues/19958)) ([ead7596](https://github.com/angular/angular/commit/ead7596))
+* **common:** remove useless guard in HttpClient ([#19958](https://github.com/angular/angular/issues/19958)) ([e099911](https://github.com/angular/angular/commit/e099911)), closes [#19223](https://github.com/angular/angular/issues/19223)
+* **common:** treat an empty body as null when parsing JSON in HttpClient ([#19958](https://github.com/angular/angular/issues/19958)) ([bdaee50](https://github.com/angular/angular/commit/bdaee50)), closes [#18680](https://github.com/angular/angular/issues/18680) [#19413](https://github.com/angular/angular/issues/19413) [#19502](https://github.com/angular/angular/issues/19502) [#19555](https://github.com/angular/angular/issues/19555)
+* **compiler-cli:** fix memory leak in program creation ([#20692](https://github.com/angular/angular/issues/20692)) ([38be44d](https://github.com/angular/angular/commit/38be44d)), closes [#20691](https://github.com/angular/angular/issues/20691)
+* **compiler-cli:** normalize sourcepaths for i18n extracted files ([#20417](https://github.com/angular/angular/issues/20417)) ([2b0c896](https://github.com/angular/angular/commit/2b0c896)), closes [#20416](https://github.com/angular/angular/issues/20416)
+
+
+
 <a name="5.0.3"></a>
 ## [5.0.3](https://github.com/angular/angular/compare/5.0.2...5.0.3) (2017-11-22)