Update bundler binstub

bin/bundle

@@ -27,7 +27,7 @@ m = Module.new do
     bundler_version = nil
     update_index = nil
     ARGV.each_with_index do |a, i|
-      if update_index && update_index.succ == i && a =~ Gem::Version::ANCHORED_VERSION_PATTERN
+      if update_index && update_index.succ == i && a.match?(Gem::Version::ANCHORED_VERSION_PATTERN)
         bundler_version = a
       end
       next unless a =~ /\A--bundler(?:[= ](#{Gem::Version::VERSION_PATTERN}))?\z/
@@ -41,13 +41,13 @@ m = Module.new do
     gemfile = ENV["BUNDLE_GEMFILE"]
     return gemfile if gemfile && !gemfile.empty?
 
-    File.expand_path("../../Gemfile", __FILE__)
+    File.expand_path("../Gemfile", __dir__)
   end
 
   def lockfile
     lockfile =
       case File.basename(gemfile)
-      when "gems.rb" then gemfile.sub(/\.rb$/, gemfile)
+      when "gems.rb" then gemfile.sub(/\.rb$/, ".locked")
       else "#{gemfile}.lock"
       end
     File.expand_path(lockfile)
@@ -60,24 +60,19 @@ m = Module.new do
     Regexp.last_match(1)
   end
 
-  def bundler_version
-    @bundler_version ||=
-      env_var_version || cli_arg_version ||
-        lockfile_version
-  end
-
   def bundler_requirement
-    return "#{Gem::Requirement.default}.a" unless bundler_version
-
-    bundler_gem_version = Gem::Version.new(bundler_version)
-
-    requirement = bundler_gem_version.approximate_recommendation
+    @bundler_requirement ||=
+      env_var_version ||
+      cli_arg_version ||
+      bundler_requirement_for(lockfile_version)
+  end
 
-    return requirement unless Gem::Version.new(Gem::VERSION) < Gem::Version.new("2.7.0")
+  def bundler_requirement_for(version)
+    return "#{Gem::Requirement.default}.a" unless version
 
-    requirement += ".a" if bundler_gem_version.prerelease?
+    bundler_gem_version = Gem::Version.new(version)
 
-    requirement
+    bundler_gem_version.approximate_recommendation
   end
 
   def load_bundler!