Add v3.20.4 to CHANGELOG.md.
Add v3.20.4 to CHANGELOG.md.

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sly7-7/ember.js,mixonic/ember.js,sandstrom/ember.js,mfeckie/ember.js,tildeio/ember.js,emberjs/ember.js,givanse/ember.js,elwayman02/ember.js,emberjs/ember.js,elwayman02/ember.js,sandstrom/ember.js,elwayman02/ember.js,mixonic/ember.js,mfeckie/ember.js,stefanpenner/ember.js,sandstrom/ember.js,stefanpenner/ember.js,mixonic/ember.js,givanse/ember.js,mfeckie/ember.js,mfeckie/ember.js,sly7-7/ember.js,emberjs/ember.js,elwayman02/ember.js,sly7-7/ember.js,givanse/ember.js,knownasilya/ember.js,givanse/ember.js,tildeio/ember.js,knownasilya/ember.js,knownasilya/ember.js,stefanpenner/ember.js,tildeio/ember.js