graphql-dotnet 发布版本: v2.2.0

#805 - performance improvements @johnrutherford

#808 - dataloader optimizations @johnrutherford

#841 - allow custom casing on inferred enum graph types @freakingawesome

#838 #839 - fixed support for list with nulls @Cooke

#859 - fix some bugs in metrics capture @joemcbride