update demo to ember-mobiledoc-editor 0.5.3
update demo to ember-mobiledoc-editor 0.5.3

bustlelabs/content-kit-editor,bustlelabs/content-kit-editor,bustlelabs/content-kit-editor,mixonic/content-kit-editor,Hstry/mobiledoc-kit,YoranBrondsema/mobiledoc-kit,bustle/mobiledoc-kit,mixonic/content-kit-editor,Hstry/mobiledoc-kit,bustle/mobiledoc-kit,bustlelabs/mobiledoc-kit,YoranBrondsema/mobiledoc-kit,bustle/mobiledoc-kit,bustlelabs/mobiledoc-kit,bustle/mobiledoc-kit,YoranBrondsema/mobiledoc-kit,Hstry/mobiledoc-kit,bustlelabs/mobiledoc-kit,mixonic/content-kit-editor