Move development dependencies to Gemfile (#124)

Author: nobu

Gemfile

@@ -4,3 +4,10 @@ git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
 # Specify your gem's dependencies in rexml.gemspec
 gemspec
+
+group :development do
+  gem "benchmark_driver"
+  gem "bundler"
+  gem "rake"
+  gem "test-unit"
+end

rexml.gemspec

@@ -56,9 +56,4 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = '>= 2.5.0'
 
   spec.add_runtime_dependency("strscan", ">= 3.0.9")
-
-  spec.add_development_dependency "benchmark_driver"
-  spec.add_development_dependency "bundler"
-  spec.add_development_dependency "rake"
-  spec.add_development_dependency "test-unit"
 end