updates import of article from article.py not article_class.py

Author: mpacer

allofplos/tests/test_corpus.py

@@ -1,6 +1,6 @@
 from . import TESTDATADIR
 from .. import Corpus, starterdir
-from ..article_class import Article
+from ..article import Article
 from ..corpus import listdir_nohidden
 
 import random