text: Title: tqdm_notebook bar malformed when bar_format is specified.
  Body: ### System Info
  
  ```sh
  >>>  import tqdm, sys
  >>>  print(tqdm.__version__, sys.version, sys.platform)
  4.28.1 3.6.7 |Anaconda, Inc.| (default, Oct 23 2018, 14:01:38) 
  [GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] darwin
  ```
  
  ### Issue:
  With the bar format below, the progress bars are correctly rendered in the terminal but incorrectly in jupyter notebook (instead of filling up the bar, another bar to the right is constructed).
  
  <img width="945" alt="screen shot 2018-12-05 at 11 59 51 am" src="https://user-images.githubusercontent.com/1762463/49540671-8590d380-f885-11e8-8b7c-649d47e94aa2.png">
  