title: "The system cannot find the file specified" when starting process using ChildProcess
body: <p>When I run the following code:</p>
  
  <pre><code>require 'childprocess'
  
  process = ChildProcess.build("cucumber")
  process.start
  </code></pre>
  
  <p>(It seem that any other gem can be instead cucumber)</p>
  
  <p>I get error:</p>
  
  <pre><code>C:/Ruby193/lib/ruby/gems/1.9.1/gems/childprocess-0.3.3/lib/childprocess/windows/process_builder.rb:87:in `create_process': The system cannot
   find the file specified. (2) (ChildProcess::LaunchError)
          from C:/Ruby193/lib/ruby/gems/1.9.1/gems/childprocess-0.3.3/lib/childprocess/windows/process_builder.rb:34:in `start'
          from C:/Ruby193/lib/ruby/gems/1.9.1/gems/childprocess-0.3.3/lib/childprocess/windows/process.rb:63:in `launch_process'
          from C:/Ruby193/lib/ruby/gems/1.9.1/gems/childprocess-0.3.3/lib/childprocess/abstract_process.rb:67:in `start'
          from env.rb:4:in `&lt;main&gt;'
  </code></pre>
  
  <p>When I run it in Windows cmd using e.g. <code>cucumber</code>, process starts normally.</p>
  
  <p>How can I solve it? Why it occurs?</p>