Wrong OptArg serialisation after OrderBy#163

### Version Information | .NET Full Framework? | 4.8 | | RethinkDB Server | 2.3.6 | Hi I have a very simple indexed orderby: ``` R.Db("db").Table("table").OrderBy().OptArg(R.Desc("lastName")).Limit(100) ``` This gives me: ``` RethinkDb.Driver.ReqlServerCompileError Expected a TermType as a NUMBER but found STRING. ``` It produces this raw string: ``` $reql_reqlraw$[71,[[41,[[15,[[14,["db"]],"table"]]],{"index":["DESC",["lastName"]]}],100]] ``` Notice the "DESC" in the raw string? Should be 74. I believe OptArgs have a serialisation bug where they use globally defined JsonConvert.Settings accidentally and therefore the enum is serialised as string. Any workarounds?