Fix a minor typo

Author: Seiichi Yonezawa

models/active_record.md

@@ -28,9 +28,9 @@ get '/' do
 end
 ```
 
-This will render ./views/index.erb:
+This will render `./views/index.erb`:
 
-```ruby
+```erb
 <% for post in @posts %>
   <h1><%= post.title %></h1>
 <% end %>

models/couchdb.md

@@ -52,9 +52,9 @@ get '/posts/:title' do
 end
 ```
 
-This will render ./views/posts.erb:
+This will render `./views/posts.erb`:
 
-```ruby
+```erb
 <% for post in @posts %>
   <div>
     <h1><%= post.title %></h1>

models/data_mapper.md

@@ -42,7 +42,7 @@ end
 
 Finally, the view at `./view/index.html`:
 
-```ruby
+```erb
 <% @posts.each do |post| %>
   <h3><%= post.title %></h3>
   <p><%= post.body %></p>

models/ohm.md

@@ -48,9 +48,9 @@ get '/posts/:title' do
 end
 ```
 
-This will render ./views/index.erb:
+This will render `./views/index.erb`:
 
-```ruby
+```erb
 <% for post in @posts %>
   <h1><%= post.title %></h1>
 <% end %>

models/sequel.md

@@ -12,6 +12,7 @@ require 'sequel'
 Use a simple in-memory DB:
 
 ```ruby
+require 'sqlite3'
 DB = Sequel.sqlite
 ```