title: Python Invoke - Can't find any collection named 'tasks'!
body: <p>I did the getting started on 
  <a href="http://docs.pyinvoke.org/en/latest/" rel="noreferrer">Python Invoke</a></p>
  
  <pre><code>from invoke import task
  
  @task
  def build():
      print("Building!")
  </code></pre>
  
  <p>The expected output is</p>
  
  <pre><code>$ invoke build
  Building!
  </code></pre>
  
  <p>However, my output is </p>
  
  <pre><code>$ invoke build
  Can't find any collection named 'tasks'!
  </code></pre>
  
  <p>I have no idea why.</p>
  
  <p>Something amazing is, once I invoke in the virtualenv, then I can build without virtualenv.</p>
  
  <pre><code>&gt; mkvirtualenv myenv
  &gt; invoke build
  Building!
  &gt; deactivate myenv
  &gt; invoke build
  Building!
  </code></pre>
  
  <p>Did I miss something?</p>