THRIFT-5349 Add net5.0 as supported platform
Client: netstd
Patch: Jens Geyer

This closes #2328
diff --git a/lib/netstd/Thrift/Collections/TCollections.cs b/lib/netstd/Thrift/Collections/TCollections.cs
index b386c37..21ee3bb 100644
--- a/lib/netstd/Thrift/Collections/TCollections.cs
+++ b/lib/netstd/Thrift/Collections/TCollections.cs
@@ -99,8 +99,7 @@
 
             foreach (var obj in enumerable)
             {
-                var enum2 = obj as IEnumerable;
-                var objHash = enum2 == null ? obj.GetHashCode() : GetHashCode(enum2);
+                var objHash = (obj is IEnumerable enum2) ? GetHashCode(enum2) : obj.GetHashCode();
 
                 unchecked
                 {