Problem when running webcam client/server demo

Hi, @jcjohnson
I followed your instruction to run the client/server webcam demo. When I am running `python webcam/server.py`, the command was stuck there and it returned

> loading checkpoint from data/models/densecap/densecap-pretrained-vgg16.t7
done loading checkpoint
Warning: cudnn.convert does not work with nngraph yet. Ignoring nn.gModule

I know the warning can be ignored safely, but I don't know the reason why the loading process was stuck(it can't run the next command)after it said `done loading checkpoint`.

And then I tried to run `python webcam/server.py`, I also have the issue

> Traceback (most recent call last):
File "webcam/server.py", line 7, in
from flask import Flask, request
ImportError: No module named flask
zhangcheng@zhangcheng-To-be-filled-by-O-E-M:~/densecap$ sudo apt-get flask
[sudo] password for zhangcheng:
E: Invalid operation flask

I appreciate your help!