Add dependencies for .NET Core in .nuspec file

Author: xplicit

NuGet/ServiceStack.Text/servicestack.text.nuspec

@@ -23,6 +23,23 @@
     <tags>JSON Text Serializer CSV JSV Dump PrettyPrint Fast</tags>
     <language>en-US</language> 
     <copyright>ServiceStack 2015 and contributors</copyright>
+    <dependencies>
+      <group targetFramework=".NETStandard1.1">
+        <dependency id="System.Linq.Expressions" version="[4.1.0, )" />
+        <dependency id="System.Runtime.Serialization.Primitives" version="[4.1.1, )" />
+        <dependency id="System.Runtime.Serialization.Xml" version="[4.1.1, )" />
+        <dependency id="System.Net.Http" version="[4.1.0, )" />
+        <dependency id="System.Net.Requests" version="[4.0.11, )" />
+        <dependency id="System.IO" version="[4.1.0, )" />
+        <dependency id="System.Dynamic.Runtime" version="[4.0.11, )" />
+        <dependency id="Microsoft.CSharp" version="[4.0.1, )" />
+        <dependency id="System.Reflection" version="[4.1.0, )" />
+        <dependency id="System.Reflection.Extensions" version="[4.0.1, )" />
+        <dependency id="System.Reflection.Emit" version="[4.0.1, )" />
+        <dependency id="System.Reflection.Emit.Lightweight" version="[4.0.1, )" />
+        <dependency id="NETStandard.Library" version="[1.6.0, )" />
+      </group>
+    </dependencies>
   </metadata>
   <files>
     <file src="lib\**\*.*" target="lib" />