Replace image_tag with lazy's one in rest of pages

Author: yasulab

app/views/shared/_header.html.haml

@@ -8,8 +8,10 @@
         %span.icon-bar
         %span.icon-bar
       .navbar-header-logos
-        = link_to image_tag('/img/header-logo.png',  alt: 'CoderDojo logo'),  '/', id: "header-logo"
-        = link_to image_tag('/img/header-brand.png', alt: 'CoderDojo brand'), '/', id: "header-brand"
+        = link_to lazy_image_tag('/img/header-logo.png',  min: '/img/header-logo.min.png',
+                                 alt: 'CoderDojo logo'),  '/', id: "header-logo"
+        = link_to lazy_image_tag('/img/header-brand.png', min: '/img/header-brand.min.png',
+                                 alt: 'CoderDojo brand'), '/', id: "header-brand"
     #bs-example-navbar-collapse-1.collapse#header-nav-toggle.navbar-collapse
       %ul.nav.navbar-nav.navbar-right
         %li= link_to '全国の道場',     '/#dojos'

app/views/spaces/index.html.haml

@@ -1,5 +1,5 @@
 %section.cover
-  = image_tag "spaces_cover.png"
+  = lazy_image_tag "spaces_cover.png", alt: "Cover photo for CoderDojo Spaces"
 
 %section.introduction.text-center.list
   %h1

app/views/stats/show.html.haml

@@ -6,7 +6,7 @@
 %script{ type: 'text/javascript', src: '/js/jquery.japan-map.js'}
 
 %section#top{style: 'padding-top:40px; background-color: white; max-width: 400px; margin: 0 auto;'}
-  = image_tag "stats_cover.png"
+  = lazy_image_tag 'stats_cover.png', alt: 'Cover photo for CoderDojo Stats'
 
 %section.stats.text-center
   %h1 統計情報