Update dependency to netstandard 2.0

was previously pulling netstandard1.3 / full framework 4.5.1, now only depends on netstandard2.0

Author: William Denton

src/Elasticsearch.Net.Aws/Elasticsearch.Net.Aws/Elasticsearch.Net.Aws.csproj

@@ -26,7 +26,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.WebUtilities" Version="1.1.2" />
+    <PackageReference Include="Microsoft.AspNetCore.WebUtilities" Version="2.1.1" />
     <PackageReference Include="AWSSDK.Core" Version="3.3.*" />
     <PackageReference Include="Elasticsearch.Net" Version="7.0.0-alpha2" />
   </ItemGroup>