Fix typo

Author: cassiersg

src/visitor.rs

@@ -353,7 +353,7 @@ impl<'a> FmtVisitor<'a> {
 
     fn format_mod(&mut self, m: &ast::Mod, s: Span, ident: ast::Ident, attrs: &[ast::Attribute]) {
         debug!("FmtVisitor::format_mod: ident: {:?}, span: {:?}", ident, s);
-        // Decide whether this is a inline mod or an external mod.
+        // Decide whether this is an inline mod or an external mod.
         // There isn't any difference between inline and external mod in AST,
         // so we use the trick of searching for an opening brace. (Tricks based
         // on inner span doesn't work in case of mod with no items.)