error in doc of quick_start (#228)

* fix error in doc of quick_start
* There are some warning when execute preprocess.sh 

demo/quick_start/preprocess.sh

@@ -20,6 +20,8 @@
 
 set -e
 
+export LC_ALL=C
+
 mkdir -p data/tmp
 python preprocess.py -i data/reviews_Electronics_5.json.gz
 # uniq and shuffle

doc/demo/quick_start/index_en.md

@@ -134,7 +134,7 @@ def process(settings, file_name):
 You need to add a data provider definition `define_py_data_sources2` in our network configuration. This definition specifies:
 
 - The path of the training and testing data (`data/train.list`, `data/test.list`).
-- The location of the data provider file (`dataprovider_pow`).
+- The location of the data provider file (`dataprovider_bow`).
 - The function to call to get data. (`process`).
 - Additional arguments or data. Here it passes the path of word dictionary.