Fix langage version (keep C# 6 for the moment)

Author: fremag

MemoScope/Core/ClrTypeError.cs

@@ -9,7 +9,7 @@ public class ClrTypeError : ClrType
         public override ulong MethodTable => 0;
         public override uint MetadataToken => 0;
         public override string Name { get; }
-        public override ClrHeap Heap => throw new NotImplementedException();
+        public override ClrHeap Heap => null;
         public override IList<ClrInterface> Interfaces => new List<ClrInterface>();
         public override bool IsFinalizable => false;
         public override bool IsPublic => false;

MemoScope/MemoScope.csproj

@@ -62,6 +62,7 @@
     <ErrorReport>prompt</ErrorReport>
     <CodeAnalysisRuleSet>MinimumRecommendedRules.ruleset</CodeAnalysisRuleSet>
     <Prefer32Bit>true</Prefer32Bit>
+    <LangVersion>6</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Release|x86'">
     <OutputPath>bin\x86\Release\</OutputPath>