Update swagger parser to 2.1.28 #161

Job	Run time
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 4s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	2m 18s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	1m 22s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	1m 20s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 15s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	1m 43s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	2m 11s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 30s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	1m 28s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 10s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 24s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	1m 4s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	1m 23s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	1m 15s
	20m 27s

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