[BUG][CSHARP][GENERICHOST] Write enum values in expected JSON format #206

Job	Run time
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 39s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	1m 17s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 7s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	59s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	1m 4s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	2m 32s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 46s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	1m 10s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	1m 20s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 6s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 11s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	1m 2s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	1m 9s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	2m 41s
	20m 3s

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