Rails 4: Use MySql and MongoDB together

I'm trying to make an application in rails 4 using MongoDB(mongoid) and MySQL together. But I'm not able to set it up.

I'm following the steps below:

1. rails new myapp -d mysql
2. Then added these lines to Gemfile:
   gem "mongoid"
gem "bson_ext"
3. bundle install
4. rails g mongoid:config

The step 4 fails. I'm not able to figure out the problem. It shows the following error.

/home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations.rb:5:in require': /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:79: syntax error, unexpected keyword_do_cond, expecting ':' @documents = attributes ? attributes.collect do |attrs| ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:84: syntax error, unexpected ':', expecting keyword_end end : [] ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:99: syntax error, unexpected keyword_do_cond, expecting keyword_end attributes.values.each do |attrs| ^ /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations/has_many.rb:139: syntax error, unexpected keyword_end, expecting end-of-input (SyntaxError) from /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid/associations.rb:5:in' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid.rb:40:in require' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/mongoid-1.0.6/lib/mongoid.rb:40:in' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:in require' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:76:inblock (2 levels) in require' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:in each' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:72:inblock in require' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:in each' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler/runtime.rb:61:inrequire' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/bundler-1.10.6/lib/bundler.rb:134:in require' from /home/devesh/fashion_hub/store/config/application.rb:7:in' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:82:in require' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:82:inpreload' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:143:in serve' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:131:inblock in run' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:125:in loop' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application.rb:125:inrun' from /home/devesh/.rvm/gems/ruby-2.2.2/gems/spring-1.3.6/lib/spring/application/boot.rb:18:in <top (required)>' from /home/devesh/.rvm/rubies/ruby-2.2.2/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:inrequire' from /home/devesh/.rvm/rubies/ruby-2.2.2/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'

I was following this url.

Some details:

1. OS - ubuntu 14.04
2. ruby v2.2.2
3. rails 4.2.3