Update 1835.md (#268)

The code didn't compile. Returning now a Task<string> instead of a Task

_rules/1835.md

@@ -6,7 +6,7 @@ severity: 1
 ---
 Consider the following asynchronous method:
 
-	private async Task GetDataAsync()
+	private async Task<string> GetDataAsync()
 	{
 		var result = await MyWebService.GetDataAsync();
 		return result.ToString();