Use jekyll-include-cache

`bundle exec jekyll build --profile`:
- before : about 130s
- after  : about 35s

Gemfile

@@ -7,5 +7,6 @@ gem 'jekyll-minifier', group: :jekyll_plugins
 gem 'jekyll-sitemap', group: :jekyll_plugins
 gem 'jekyll-last-modified-at', group: :jekyll_plugins
 gem 'jekyll-tagging', group: :jekyll_plugins
+gem 'jekyll-include-cache', group: :jekyll_plugins
 gem 'nokogiri'
 gem 'fastimage'

Gemfile.lock

@@ -33,6 +33,8 @@ GEM
       safe_yaml (~> 1.0)
     jekyll-compose (0.11.0)
       jekyll (>= 3.7, < 5.0)
+    jekyll-include-cache (0.2.0)
+      jekyll (>= 3.7, < 5.0)
     jekyll-last-modified-at (1.1.0)
       jekyll (>= 3.7, < 5.0)
       posix-spawn (~> 0.3.9)
@@ -90,6 +92,7 @@ DEPENDENCIES
   fastimage
   jekyll
   jekyll-compose
+  jekyll-include-cache
   jekyll-last-modified-at
   jekyll-minifier
   jekyll-paginate

_config.yml

@@ -48,6 +48,7 @@ kramdown:
 plugins:
 - jekyll-paginate
 - jekyll-last-modified-at
+- jekyll-include-cache
 
 permalink: /:categories/:year-:month-:day-:title.html
 strict_front_matter: true

_includes/amp-custom.html

@@ -0,0 +1,7 @@
+<style amp-custom>
+ {% capture include_to_scssify %}
+ {% include styles.scss %}
+ {% include custom.scss %}
+ {% endcapture %}
+ {{ include_to_scssify | scssify }}
+</style>

_includes/head.html

@@ -42,15 +42,7 @@
   </script>
 
   <link href="https://use.fontawesome.com/releases/v5.5.0/css/all.css" rel="stylesheet">
-  <style amp-custom>
-  {% capture include_to_scssify %}
-    {% include styles.scss %}
-    {% include custom.scss %}
-  {% endcapture %}
-  {{ include_to_scssify | scssify }}
-  </style>
-
-
+  {% include_cached amp-custom.html %}
 
   <style amp-boilerplate>body{-webkit-animation:-amp-start 8s steps(1,end) 0s 1 normal both;-moz-animation:-amp-start 8s steps(1,end) 0s 1 normal both;-ms-animation:-amp-start 8s steps(1,end) 0s 1 normal both;animation:-amp-start 8s steps(1,end) 0s 1 normal both}@-webkit-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-moz-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-ms-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-o-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}</style><noscript><style amp-boilerplate>body{-webkit-animation:none;-moz-animation:none;-ms-animation:none;animation:none}</style></noscript>
   <script async src="https://cdn.ampproject.org/v0.js"></script>