chore(speech-to-text-v1): revert JsonSubTypes version

Author: kevinkowa

src/IBM.Watson.SpeechToText.v1/IBM.Watson.SpeechToText.v1.csproj

@@ -37,7 +37,7 @@
         <PackageReference Include="IBM.Cloud.SDK.Core" Version="1.2.0" />
         <PackageReference Include="IBM.Watson.Common" Version="5.2.0" />
         <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
-        <PackageReference Include="JsonSubTypes" Version="1.6.0" />
+        <PackageReference Include="JsonSubTypes" Version="1.8.0" />
     </ItemGroup>
 
 </Project>