Lowering .net 6 to .net 5

Author: Matt Hunt

src/GeoJSON.Net/GeoJSON.Net.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard1.0;netstandard1.1;netstandard2.0;netstandard2.1;net40;net45;net6.0</TargetFrameworks>
+    <TargetFrameworks>netstandard1.0;netstandard1.1;netstandard2.0;netstandard2.1;net40;net45;net5.0</TargetFrameworks>
     <Description>.Net types for the GeoJSON RFC to be used with Json.Net</Description>
     <Authors>Matt Hunt;Joerg Battermann;Xavier Fischer</Authors>
     <Company>GeoJSON.Net</Company>