THRIFT-5252 Make CreateHttpClientHandler() method virtual
Client: netstd
Patch: Jens Geyer

This closes #2201
diff --git a/lib/netstd/Thrift/Transport/Client/THttpTransport.cs b/lib/netstd/Thrift/Transport/Client/THttpTransport.cs
index 7b4514f..dcd028c 100644
--- a/lib/netstd/Thrift/Transport/Client/THttpTransport.cs
+++ b/lib/netstd/Thrift/Transport/Client/THttpTransport.cs
@@ -168,7 +168,7 @@
         /// A client handler with deflate and gZip compression-decompression algorithms and any client
         /// certificates passed in via <c>certificates</c>.
         /// </returns>
-        public static HttpClientHandler CreateHttpClientHandler(X509Certificate[] certificates = null)
+        public virtual HttpClientHandler CreateHttpClientHandler(X509Certificate[] certificates = null)
         {
             var handler = new HttpClientHandler();
             if (certificates != null)