fix the title of intro

ocha- · ocha- · commit 0ac55c0f586e · 2013-09-12T09:41:09.000+09:00
diff --git a/intro.textile b/intro.textile
@@ -1,9 +1,10 @@
 ---
 layout: default
+title: Introduction
 ---
 
 
-h1. Preface: Introduction
+h1. Introduction
 
 h2. Characteristics of Ruby
 
