Fixed MissingMethodException for HostBuilderContext.get_HostingEnvironment() (#599)

Author: snakefoot

src/NLog.Extensions.Hosting/Extensions/ConfigureExtensions.cs

@@ -38,7 +38,11 @@ public static IHostBuilder UseNLog(this IHostBuilder builder)
         public static IHostBuilder UseNLog(this IHostBuilder builder, NLogProviderOptions options)
         {
             if (builder == null) throw new ArgumentNullException(nameof(builder));
+#if NETSTANDARD2_0
+            builder.ConfigureServices((builderContext, services) => AddNLogLoggerProvider(services, builderContext.Configuration, null, options, CreateNLogLoggerProvider));
+#else
             builder.ConfigureServices((builderContext, services) => AddNLogLoggerProvider(services, builderContext.Configuration, builderContext.HostingEnvironment, options, CreateNLogLoggerProvider));
+#endif
             return builder;
         }