Update csharp.html.markdown

fix #4895

csharp.html.markdown

@@ -867,7 +867,7 @@ on a new line! ""Wow!"", the masses cried";
         }
 
         // It's also possible to define custom Indexers on objects.
-        // All though this is not entirely useful in this example, you
+        // Although this is not entirely useful in this example, you
         // could do bicycle[0] which returns "chris" to get the first passenger or
         // bicycle[1] = "lisa" to set the passenger. (of this apparent quattrocycle)
         private string[] passengers = { "chris", "phil", "darren", "regina" };