Add 0.4.21 to the changelog
Add 0.4.21 to the changelog

apollographql/apollo-client,apollostack/apollo-client,cesarsolorzano/apollo-client,stevewillard/apollo-client,calebmer/apollo-client,apollographql/apollo-client,cesarsolorzano/apollo-client,apollostack/apollo-client,stevewillard/apollo-client,cesarsolorzano/apollo-client,apollostack/apollo-client,calebmer/apollo-client,stevewillard/apollo-client,calebmer/apollo-client