title: Warning: this Gemfile contains multiple primary sources during vagrant-rsync-back plugin Installation
body: <p>I installed <code>vargrant</code> in my windows 7, my VM box is <code>CentOS</code> 6, well vagrant is working fine.But now I want to install <code>rsync-back</code> for syncing my VM files to Windows, I am getting few errors.</p>
  
  <p>When I use the command in CMD windows,</p>
  
  <pre><code>vagrant plugin install vagrant-rsync-back
  </code></pre>
  
  <p>I get the below errors</p>
  
  <blockquote>
    <p>Installing the 'vagrant-rsync-back' plugin. This can take a few
    minutes... Bundler, the underlying system Vagrant uses to install
    plugins, reported an error. The error is shown below. These errors are
    usually caused by misconfigured plugin installations or transient
    network issues. The error from Bundler is:</p>
    
    <p>Could not fetch specs from <a href="http://gems.hashicorp.com/" rel="nofollow">http://gems.hashicorp.com/</a></p>
    
    <p>Warning: this Gemfile contains multiple primary sources. Using
    <code>source</code> more than once without a block is a security risk, and may
    result in installing unexpected gems. T o resolve this warning, use a
    block to indicate which gems should come from the secondary source. To
    upgrade this warning to an error, run <code>bundle config disable_multisou
    rce true</code>.</p>
  </blockquote>
  
  <p>I am pretty new to vagrant, I am unable to solve this issue. Any suggestion where I am doing wrong ?</p>