refactored CombineStep.cs removed redundant ToString call (#785)

* refactored CombineStep.cs removed redundant ToString call

* refactored CombineStep.cs applied string interpolation feature

* refactored CombineStep.cs use of language feature

src/Microsoft.Tye.Core/CombineStep.cs

@@ -39,7 +39,7 @@ namespace Microsoft.Tye
                 if (binding.Protocol == "http")
                 {
                     var port = binding.ContainerPort ?? binding.Port ?? 80;
-                    var urls = $"http://*{(port == 80 ? "" : (":" + port.ToString()))}";
+                    var urls = $"http://*{(port == 80 ? "" : $":{port}")}";
                     project.EnvironmentVariables.Add(new EnvironmentVariableBuilder("ASPNETCORE_URLS") { Value = urls, });
                     project.EnvironmentVariables.Add(new EnvironmentVariableBuilder("PORT") { Value = port.ToString(CultureInfo.InvariantCulture), });
                     break;
@@ -95,10 +95,7 @@ namespace Microsoft.Tye
                             continue;
                         }
 
-                        if (binding.Protocol == null)
-                        {
-                            binding.Protocol = "http";
-                        }
+                        binding.Protocol ??= "http";
 
                         if (binding.Port == null && binding.Protocol == "http")
                         {