OperationContractAttribute not available in netcore2.1

[CalvinPangch]

by refering the feeback from dotnet core in the links
dotnet/core#1966

the OperationContractAttribute is available in netcore2.1, please correct the doc. Thanks

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 74df8a99-6bfb-f551-92b5-394d7852b198
• Version Independent ID: 295c3462-ebbe-0d19-ff0d-f8ea2fec6b0f
• Content: OperationContractAttribute Class (System.ServiceModel)
• Content Source: xml/System.ServiceModel/OperationContractAttribute.xml
• Product: dotnet-api
• GitHub Login: @dotnet-bot
• Microsoft Alias: dotnetcontent

[Thraka]

@mairaw in the linked issue, this was confirmed by @MarcoRossignoli

Not sure how we fix this type of issue.

[mairaw]

I gave some details here: dotnet/core#1966 (comment)

[mairaw]

@safern we'll need your help figuring this one out. API Catalog doesn't show this one as part of .NET Core at all: https://apisof.net/catalog/System.ServiceModel.OperationContractAttribute

And it shows this being available for Platform extensions since 2.0 but we're still missing BCL platform extensions for 2.0 and earlier in the docs.

/cc @BillWagner