Added netstandard2.0 as a target framework

Author: danjagnow

src/Serilog.Enrichers.Thread/Serilog.Enrichers.Thread.csproj

@@ -1,10 +1,10 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <Description>Enrich Serilog events with properties from the current thread.</Description>
     <VersionPrefix>3.0.1</VersionPrefix>
     <Authors>Serilog Contributors</Authors>
-    <TargetFrameworks>net45;netstandard1.0</TargetFrameworks>
+    <TargetFrameworks>net45;netstandard1.0;netstandard2.0</TargetFrameworks>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <AssemblyName>Serilog.Enrichers.Thread</AssemblyName>