Fixed typo in readme

README.md

@@ -113,7 +113,7 @@ gulp.task('default', ['compile']);
 
 **extend**: [function (Twig)] *extends Twig with new tags types. The Twig attribute is Twig.js's internal object. [Read more here](https://github.com/justjohn/twig.js/wiki/Extending-twig.js-With-Custom-Tags)*
 
-**extname**: [string|true|false] *output file extension including the '.' like path.extname(filename). Use `true` to keep source extname and `false` to drop the file extensionS*
+**extname**: [string|true|false] *output file extension including the '.' like path.extname(filename). Use `true` to keep source extname and a "falsy" value to drop the file extension*
 
 **functions**: [array] *extends Twig with given function objects. (default to undefined)*
 ```javascript