Fix a tyop

Author: vitaut

Text Formatting.html

@@ -324,8 +324,8 @@ <h3><a name="Syntax">Format string syntax</a></h3>
 </p>
 
 <p>
-In addition to positional argument, the grammar can be esily extended to support
-named arguments.
+In addition to positional arguments, the grammar can be easily extended to
+support named arguments.
 </p>
 
 <h3><a name="Extensibility">Extensibility</a></h3>