Fixing unclosed file warnings

[alex-wearisma]

Hello,

There are some open() calls which are not closed after the use. Leaving file handles open leaks resources and makes Python raise warning such as the one bellow:

/Users/coder/project/extract.py:72: ResourceWarning: unclosed file <_io.BufferedReader name='/Users/coder/project/resources/keywords/zh/userdict.txt'>
  jieba.load_userdict(str(p))
ResourceWarning: Enable tracemalloc to get the object allocation traceback

This change closes all open file handles.

This change should also solve issue reported here: #546 .

Thank you!