update FQA of matplotlib

Author: zsdonghao

docs/user/more.rst

@@ -81,7 +81,7 @@ If you run the script via SSH control, sometime you may find the following error
 
   _tkinter.TclError: no display name and no $DISPLAY environment variable
 
-If happen, ``import matplotlib matplotlib.use('Agg')`` before import ``tensorlayer as tl``.
+If happen, use ``import matplotlib`` and ``matplotlib.use('Agg')`` before ``import tensorlayer as tl``.
 Alternatively, add the following code into the top of ``visualize.py``.
 
 .. code-block:: python