app: update code to Rails 6.1

bin/spring

@@ -1,17 +1,14 @@
 #!/usr/bin/env ruby
+if !defined?(Spring) && [nil, "development", "test"].include?(ENV["RAILS_ENV"])
+  gem "bundler"
+  require "bundler"
 
-# This file loads spring without using Bundler, in order to be fast.
-# It gets overwritten when you run the `spring binstub` command.
-
-unless defined?(Spring)
-  require 'rubygems'
-  require 'bundler'
-
-  lockfile = Bundler::LockfileParser.new(Bundler.default_lockfile.read)
-  spring = lockfile.specs.detect { |spec| spec.name == "spring" }
-  if spring
+  # Load Spring without loading other gems in the Gemfile, for speed.
+  Bundler.locked_gems.specs.find { |spec| spec.name == "spring" }&.tap do |spring|
     Gem.use_paths Gem.dir, Bundler.bundle_path.to_s, *Gem.path
-    gem 'spring', spring.version
-    require 'spring/binstub'
+    gem "spring", spring.version
+    require "spring/binstub"
+  rescue Gem::LoadError
+    # Ignore when Spring is not installed.
   end
 end