Fix high cognitive complexity of Changelog#to_s (#20)

Author: jcouball

lib/create_github_release/changelog.rb

@@ -292,15 +292,28 @@ def body
     #
     def to_s
       String.new.tap do |changelog|
-        changelog << "#{front_matter}\n\n" unless front_matter.empty?
-        changelog << release_header
-        changelog << release_description
-        changelog << "\n#{body}\n" unless body.empty?
+        changelog << formatted_front_matter unless front_matter.empty?
+        changelog << release_header << release_description
+        changelog << formatted_body unless body.empty?
       end
     end
 
     private
 
+    # The front matter formatted to insert into the changelog
+    # @return [String] The front matter formatted to insert into the changelog
+    # @api private
+    def formatted_front_matter
+      "#{front_matter}\n\n"
+    end
+
+    # The body formatted to insert into the changelog
+    # @return [String] The body formatted to insert into the changelog
+    # @api private
+    def formatted_body
+      "\n#{body}\n"
+    end
+
     # The index of the line in @lines where the front matter begins
     # @return [Integer] The index of the line in @lines where the front matter begins
     # @api private