Require bundler >= 1.5.0 (#19172).

git-svn-id: http://svn.redmine.org/redmine/trunk@14065 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -1,5 +1,9 @@
 source 'https://rubygems.org'
 
+if Gem::Version.new(Bundler::VERSION) < Gem::Version.new('1.5.0')
+  abort "Redmine requires Bundler 1.5.0 or higher (you're using #{Bundler::VERSION}).\nPlease update with 'gem update bundler'." 
+end
+
 gem "rails", "4.2.0"
 gem "jquery-rails", "~> 3.1.1"
 gem "coderay", "~> 1.1.0"