diff --git a/.rubocop.yml b/.rubocop.yml
index adb0ca87..8c90c049 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -10,7 +10,6 @@ AllCops:
   - lib/jekyll/document.rb
   - lib/jekyll/regenerator.rb
   - lib/jekyll/renderer.rb
-  - lib/jekyll/static_file.rb
   - lib/jekyll/utils.rb
   - bin/**/*
   - benchmark/**/*
diff --git a/lib/jekyll/static_file.rb b/lib/jekyll/static_file.rb
index 3e7d0d25..0f8544ee 100644
--- a/lib/jekyll/static_file.rb
+++ b/lib/jekyll/static_file.rb
@@ -1,16 +1,25 @@
 module Jekyll
   class StaticFile
-    # The cache of last modification times [path] -> mtime.
-    @@mtimes = {}
-
     attr_reader :relative_path, :extname
 
+    class << self
+      # The cache of last modification times [path] -> mtime.
+      def mtimes
+        @mtimes ||= {}
+      end
+
+      def reset_cache
+        @mtimes = nil
+      end
+    end
+
     # Initialize a new StaticFile.
     #
     # site - The Site.
     # base - The String path to the <source>.
     # dir  - The String path between <source> and the file.
     # name - The String filename of the file.
+    # rubocop: disable ParameterLists
     def initialize(site, base, dir, name, collection = nil)
       @site = site
       @base = base
@@ -20,6 +29,7 @@ module Jekyll
       @relative_path = File.join(*[@dir, @name].compact)
       @extname = File.extname(@name)
     end
+    # rubocop: enable ParameterLists
 
     # Returns source file path.
     def path
@@ -56,7 +66,7 @@ module Jekyll
     #
     # Returns true if modified since last write.
     def modified?
-      @@mtimes[path] != mtime
+      self.class.mtimes[path] != mtime
     end
 
     # Whether to write the file to the filesystem
@@ -64,7 +74,7 @@ module Jekyll
     # Returns true unless the defaults for the destination path from
     # _config.yml contain `published: false`.
     def write?
-      defaults.fetch('published', true)
+      defaults.fetch("published", true)
     end
 
     # Write the static file to the destination directory (if modified).
@@ -76,28 +86,15 @@ module Jekyll
       dest_path = destination(dest)
 
       return false if File.exist?(dest_path) && !modified?
-      @@mtimes[path] = mtime
+      self.class.mtimes[path] = mtime
 
       FileUtils.mkdir_p(File.dirname(dest_path))
       FileUtils.rm(dest_path) if File.exist?(dest_path)
-      if @site.safe || Jekyll.env == "production"
-        FileUtils.cp(path, dest_path)
-      else
-        FileUtils.copy_entry(path, dest_path)
-      end
-      File.utime(@@mtimes[path], @@mtimes[path], dest_path)
+      copy_file(dest_path)
 
       true
     end
 
-    # Reset the mtimes cache (for testing purposes).
-    #
-    # Returns nothing.
-    def self.reset_cache
-      @@mtimes = {}
-      nil
-    end
-
     def to_liquid
       {
         "extname"       => extname,
@@ -109,11 +106,11 @@ module Jekyll
     def placeholders
       {
         :collection => @collection.label,
-        :path => relative_path[
+        :path       => relative_path[
           @collection.relative_directory.size..relative_path.size],
-        :output_ext => '',
-        :name => '',
-        :title => ''
+        :output_ext => "",
+        :name       => "",
+        :title      => ""
       }
     end
 
@@ -125,10 +122,10 @@ module Jekyll
                  relative_path
                else
                  ::Jekyll::URL.new({
-                   :template => @collection.url_template,
+                   :template     => @collection.url_template,
                    :placeholders => placeholders
                  })
-               end.to_s.gsub(/\/$/, '')
+               end.to_s.gsub(%r!/$!, "")
     end
 
     # Returns the type of the collection if present, nil otherwise.
@@ -141,5 +138,15 @@ module Jekyll
     def defaults
       @defaults ||= @site.frontmatter_defaults.all url, type
     end
+
+    private
+    def copy_file(dest_path)
+      if @site.safe || Jekyll.env == "production"
+        FileUtils.cp(path, dest_path)
+      else
+        FileUtils.copy_entry(path, dest_path)
+      end
+      File.utime(self.class.mtimes[path], self.class.mtimes[path], dest_path)
+    end
   end
 end