Jim Schubert bc8fe0fd03 [csharp] date proper format (#5734) ...

* [csharp] Honor Swagger/OpenAPI 'date' format

Per spec
(https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#data-types),
DateTime instances defined as 'date' datatype need to be serialized as
defined by full-date - RFC3339, which has the format:

full-date       = date-fullyear "-" date-month "-" date-mday

ref:
https://xml2rfc.tools.ietf.org/public/rfc/html/rfc3339.html#anchor14

see #5513
see #5531

* [csharp] Regenerate sample

* [csharp] Include date format test

2017-06-05 00:57:00 +08:00

..

IO.Swagger

[csharp] date proper format (#5734)

2017-06-05 00:57:00 +08:00

IO.Swagger.Test

[csharp] date proper format (#5734)

2017-06-05 00:57:00 +08:00