Moved async functions for ES6 behind experimental flag

src/compiler/commandLineParser.ts

@@ -192,6 +192,11 @@ namespace ts {
             type: "boolean",
             description: Diagnostics.Watch_input_files,
         },
+        {
+            name: "experimentalAsyncFunctions",
+            type: "boolean",
+            description: Diagnostics.Enables_experimental_support_for_ES7_async_functions
+        },
         {
             name: "experimentalDecorators",
             type: "boolean",