write_xlsx.gemspec in write_xlsx-0.81.1 vs write_xlsx.gemspec in write_xlsx-0.83.0

@@ -18,9 +18,10 @@
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ["lib"]
   gem.add_runtime_dependency 'rubyzip', '>= 1.0.0'
   gem.add_runtime_dependency 'zip-zip'
   gem.add_development_dependency 'test-unit'
+  gem.add_development_dependency 'rake'
   gem.extra_rdoc_files = [
     "LICENSE.txt",
     "README.md",
     "Changes"
   ]