Fix Newtonsoft.Json NuGet dependency

Fixes #254

Author: RTLcoil

CloudinaryDotNet.nuspec

@@ -16,17 +16,20 @@
     <tags>Image Video Responsive Web Utility CDN Performance Resize Crop Rotate Quality Watermark Gif Jpg Jpeg Bitmap PNG Tiff Webp Webm mp4 avi Filter Effect</tags>
     <dependencies>
       <group>
-        <dependency id="Newtonsoft.Json" version="12.0.1" />
+        <dependency id="Newtonsoft.Json" version="12.0.3" />
       </group>
       <group targetFramework="net45">
         <dependency id="System.Runtime.InteropServices.RuntimeInformation" version="4.3.0" />
         <dependency id="System.Globalization" version="4.3.0" />
         <dependency id="System.Text.Encodings.Web" version="4.5.0" />
+        <dependency id="Newtonsoft.Json" version="12.0.3" />
       </group>
       <group targetFramework="netstandard1.3">
+        <dependency id="Newtonsoft.Json" version="12.0.3" />
       </group>
       <group targetFramework="netstandard2.0">
-      </group>    
+        <dependency id="Newtonsoft.Json" version="12.0.3" />
+      </group>
     </dependencies>
   </metadata>
   <files>