title: Deprecation error when using imageio.ffmpeg.download()
body: <p>I'm trying to merge the prerecorded videos using python Opencv.
  But i'm getting the error while importing.</p>
  
  <pre><code>"Traceback (most recent call last):
    File "video.py", line 4, in &lt;module&gt;
      from moviepy. editor import VideoFileClip,concatenate_videoclips 
    File "/home/pi/.virtualenvs/cv/lib/python3.5/site-packages/moviepy/editor.py", line 26, in &lt;module&gt;
      imageio.plugins.ffmpeg.download()
    File "/home/pi/.virtualenvs/cv/lib/python3.5/site-packages/imageio/plugins/ffmpeg.py", line 40, in download
      "imageio.ffmpeg.download() has been deprecated. "
  RuntimeError: imageio.ffmpeg.download() has been deprecated. Use 'pip install imageio-ffmpeg' instead.'"
  </code></pre>
  
  <p>would anyone please help to get out of this problem</p>
  
  <p>Here is the code:</p>
  
  <pre><code>import cv2 
  import os 
  import time 
  from moviepy.editor import VideoFileClip,concatenate_videoclips 
  def vidcapt():
      a = time.strftime("%H,%M,%S")
      cap = cv2.VideoCapture(0)
      fourcc = cv2.VideoWriter_fourcc(*'XVID')
      out = cv2.VideoWriter(a+'.avi', fourcc, 24.0, (640,480))
      t1 = time.time()
      while(cap.isOpened()):
              ret, frame = cap.read() 
              if ret == True:
                      out.write(frame)
                      cv2.imshow('frame',frame)
                      t2 = time.time()
                      time_diff = t2-t1
                      if time_diff &gt;= 5:
                              break
              else:
                      break
      cap.release()
      out.release()
      cv2.destroyAllWindows()
  
  while True:
          vidcapt()
  
  
  clip1 = VideoFileClip("11,05,42.avi")
  clip2 = VideoFileClip("11,05,47.avi").subclip(50,60)
  final_clip = concatenate_videoclips([clip1,clip2])
  final_clip.write_videofile("merged.avi")
  </code></pre>