fix: csharp example RandomWriter does not build

CDK and JSII versions were not pinned and the latest release included breaking changes.
Also modified the dependencies to be pinned to the latest version

csharp/random-writer/src/RandomWriter/RandomWriter.csproj

@@ -2,16 +2,16 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Amazon.CDK" Version="*" />
-    <PackageReference Include="Amazon.CDK.AWS.DynamoDb" Version="*" />
-    <PackageReference Include="Amazon.CDK.AWS.Events" Version="*" />
-    <PackageReference Include="Amazon.CDK.AWS.Events.Targets" Version="*" />
-    <PackageReference Include="Amazon.CDK.AWS.Lambda" Version="*" />
+    <PackageReference Include="Amazon.CDK" Version="1.31.0" />
+    <PackageReference Include="Amazon.CDK.AWS.DynamoDb" Version="1.31.0" />
+    <PackageReference Include="Amazon.CDK.AWS.Events" Version="1.31.0" />
+    <PackageReference Include="Amazon.CDK.AWS.Events.Targets" Version="1.31.0" />
+    <PackageReference Include="Amazon.CDK.AWS.Lambda" Version="1.31.0" />
 
-    <PackageReference Include="Amazon.JSII.Analyzers" Version="*" />
+    <PackageReference Include="Amazon.JSII.Analyzers" Version="1.1.0" />
   </ItemGroup>
 </Project>