Use the same version of nokogiri in example app

... to fix the installation problem on Travis CI.

Author: yujinakayama

example_app_generator/generate_app.rb

@@ -1,3 +1,5 @@
+require 'nokogiri/version'
+
 rspec_rails_repo_path = File.expand_path("../../", __FILE__)
 rspec_dependencies_gemfile = File.join(rspec_rails_repo_path, 'Gemfile-rspec-dependencies')
 rails_dependencies_gemfile = File.join(rspec_rails_repo_path, 'Gemfile-rails-dependencies')
@@ -15,6 +17,10 @@
   # edge branches
   gsub_file 'Gemfile', /^.*\bgem 'rails.*$/, ''
 
+  # Nokogiri version is pinned in rspec-rails' Gemfile since it tend to cause installation problems
+  # on Travis CI, so we pin nokogiri in this example app also.
+  append_to_file 'Gemfile', "gem 'nokogiri', '#{Nokogiri::VERSION}'\n"
+
   # Use our version of RSpec and Rails
   append_to_file 'Gemfile', <<-EOT.gsub(/^ +\|/, '')
     |# Rack::Cache 1.3.0 requires Ruby >= 2.0.0