Add netcoreapp2.1 target

Author: asbjornu

src/json-ld.net/json-ld.net.csproj

@@ -5,7 +5,7 @@
 Implements the W3C JSON-LD 1.0 standard.</Description>
     <VersionPrefix>1.0.6</VersionPrefix>
     <Authors>NuGet;linked-data-dotnet</Authors>
-    <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard1.3;netstandard2.0;netcoreapp2.1</TargetFrameworks>
     <AssemblyName>json-ld.net</AssemblyName>
     <PackageId>json-ld.net</PackageId>
     <PackageTags>json-ld;jsonld;json;linked-data;rdf;semantic;web</PackageTags>