Use Jekyll::Cache to cache template

https://github.com/jekyll/jekyll/pull/7136

lib/jekyll-seo-tag.rb

@@ -54,8 +54,13 @@ module Jekyll
       })
     end
 
+    # The `drop` should not be cached since there is going to be just
+    # one instance of this class per `{% seo %}`
+    # i.e., if you're going to use `{% seo %}` in two templates that are
+    # collectively used by 50 documents, there's just going to be
+    # **2 instances of this class** instead of a **100**.
     def drop
-      @drop ||= Jekyll::SeoTag::Drop.new(@text, @context)
+      Jekyll::SeoTag::Drop.new(@text, @context)
     end
 
     def info
@@ -67,7 +72,9 @@ module Jekyll
 
     class << self
       def template
-        @template ||= Liquid::Template.parse template_contents
+        @template ||= Jekyll::Cache.new("jekyll-seo-tag").getset("template") do
+          Liquid::Template.parse template_contents
+        end
       end
 
       private