Move required development gems directly to Gemfile

This is considered more idiomatic, and gets flagged by newer Rubocop
versions.

Author: lfittl

Gemfile

@@ -1,3 +1,9 @@
 source 'https://rubygems.org'
 
 gemspec
+
+gem 'rake-compiler', '~> 0'
+gem 'rspec', '~> 3.0'
+gem 'rubocop', '0.49.1'
+gem 'rubocop-rspec', '1.15.1'
+gem 'simplecov', '~> 0'

pg_query.gemspec

@@ -25,10 +25,5 @@ Gem::Specification.new do |s|
   s.rdoc_options     = %w[--main README.md --exclude ext/]
   s.extra_rdoc_files = %w[CHANGELOG.md README.md]
 
-  s.add_development_dependency 'rake-compiler', '~> 0'
-  s.add_development_dependency 'rspec', '~> 3.0'
-  s.add_development_dependency 'rubocop', '0.49.1'
-  s.add_development_dependency 'rubocop-rspec', '1.15.1'
-  s.add_development_dependency 'simplecov', '~> 0'
   s.add_dependency 'google-protobuf', '>= 3.25.3'
 end