change back to LangVersion 9.0

Author: Oceania2018

src/TensorFlowNET.Core/Tensorflow.Binding.csproj

@@ -6,7 +6,7 @@
     <RootNamespace>Tensorflow</RootNamespace>
     <TargetTensorFlow>2.2.0</TargetTensorFlow>
     <Version>0.60.5</Version>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>9.0</LangVersion>
     <Nullable>enable</Nullable>
     <Authors>Haiping Chen, Meinrad Recheis, Eli Belash</Authors>
     <Company>SciSharp STACK</Company>

src/TensorFlowNET.Keras/Tensorflow.Keras.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <AssemblyName>Tensorflow.Keras</AssemblyName>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>9.0</LangVersion>
     <Nullable>enable</Nullable>
     <RootNamespace>Tensorflow.Keras</RootNamespace>
     <Platforms>AnyCPU;x64</Platforms>