Add v3.4.0-beta.2 to CHANGELOG

[ci skip]

(cherry picked from commit df84704)

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Ember Changelog
 
+### v3.4.0-beta.2 (August 06, 2018)
+
+- [#16857](https://github.com/emberjs/ember.js/pull/16857) [BUGFIX] Prevents the recursive redefinition of root chains
+- [#16854](https://github.com/emberjs/ember.js/pull/16854) [BUGFIX] Don't thread FactoryManager through createComponent
+- [#16853](https://github.com/emberjs/ember.js/pull/16853) [BUGFIX] Allow ArrayProxy#pushObjects to accept ArrayProxy again
+
 ### v3.4.0-beta.1 (July 16, 2018)
 
 - [#16773](https://github.com/emberjs/ember.js/pull/16773) [FEATURE] Custom component manager (see [emberjs/rfcs#213](https://github.com/emberjs/rfcs/blob/master/text/0213-custom-components.md) for more details)