Bump Microsoft.AspNetCore.Server.Kestrel.Core (#769)

Bumps [Microsoft.AspNetCore.Server.Kestrel.Core](https://github.com/aspnet/AspNetCore) from 2.1.3 to 2.1.7.
- [Release notes](https://github.com/aspnet/AspNetCore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](dotnet/aspnetcore@2.1.3...v2.1.7)

---
updated-dependencies:
- dependency-name: Microsoft.AspNetCore.Server.Kestrel.Core
  dependency-type: direct:production
...

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examples/WireMock.Net.StandAlone.Net461/packages.config

@@ -24,7 +24,7 @@
   <package id="Microsoft.AspNetCore.Routing.Abstractions" version="2.1.1" targetFramework="net461" />
   <package id="Microsoft.AspNetCore.Server.IISIntegration" version="2.1.2" targetFramework="net461" />
   <package id="Microsoft.AspNetCore.Server.Kestrel" version="2.1.3" targetFramework="net461" />
-  <package id="Microsoft.AspNetCore.Server.Kestrel.Core" version="2.1.3" targetFramework="net461" />
+  <package id="Microsoft.AspNetCore.Server.Kestrel.Core" version="2.1.7" targetFramework="net461" />
   <package id="Microsoft.AspNetCore.Server.Kestrel.Https" version="2.1.3" targetFramework="net461" />
   <package id="Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions" version="2.1.3" targetFramework="net461" />
   <package id="Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets" version="2.1.3" targetFramework="net461" />