Prepare changelog for v0.8.4-rc.2
Prepare changelog for v0.8.4-rc.2

martindale/vector,martindale/vector,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,vector-im/vector-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web