Implicitly skip spring for `rails new --dev`

Spring seems like an obvious foot gun for the `--dev` setup, presumably you are
about to make lots of changes to the codebase, so it should always reload the
framework.

railties/lib/rails/generators/app_base.rb

@@ -336,7 +336,7 @@ def bundle_install?
       end
 
       def spring_install?
-        !options[:skip_spring] && Process.respond_to?(:fork) && !RUBY_PLATFORM.include?("cygwin")
+        !options[:skip_spring] && !options.dev? && Process.respond_to?(:fork) && !RUBY_PLATFORM.include?("cygwin")
       end
 
       def run_bundle

railties/test/generators/app_generator_test.rb

@@ -560,6 +560,14 @@ def test_skip_spring
     end
   end
 
+  def test_spring_with_dev_option
+    run_generator [destination_root, "--dev"]
+
+    assert_file "Gemfile" do |content|
+      assert_no_match(/spring/, content)
+    end
+  end
+
   def test_generator_if_skip_turbolinks_is_given
     run_generator [destination_root, "--skip-turbolinks"]