Move rake development dependency to Gemfile

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: fletchto99

Gemfile

@@ -10,6 +10,7 @@ group :test do
   gem "json"
   gem "pry-nav"
   gem "rack"
+  gem "rake"
   gem "rspec"
   gem "rubocop"
   gem "rubocop-github"

secure_headers.gemspec

@@ -30,6 +30,4 @@ Gem::Specification.new do |gem|
   gem.extra_rdoc_files = Dir["README.md", "CHANGELOG.md", "LICENSE"]
 
   gem.add_dependency "cgi", ">= 0.1"
-
-  gem.add_development_dependency "rake"
 end