Misc cleanups

Source/Framework/Dynamic/OptionalType.cs

@@ -28,7 +28,7 @@ namespace Framework.Dynamic
             set
             {
                 _hasValue = value;
-                Value = _hasValue ? new T() : default(T);
+                Value = _hasValue ? new T() : default;
             }
         }
 
@@ -41,7 +41,7 @@ namespace Framework.Dynamic
         public void Clear()
         {
             _hasValue = false;
-            Value = default(T);
+            Value = default;
         }
 
         public static explicit operator T(Optional<T> value)

Source/Framework/Framework.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>netstandard2.1</TargetFramework>
 	<Platforms>x64</Platforms>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <LangVersion>8.0</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

Source/Framework/GameMath/Plane.cs

@@ -253,7 +253,7 @@ namespace Framework.GameMath
         /// <returns>A string representation of this object.</returns>
         public override string ToString()
         {
-            return $"Plane[n={_normal.ToString()}, c={_const.ToString()}]";
+            return $"Plane[n={_normal}, c={_const}]";
         }
         #endregion
     }