StopIteration error in Python 3.7

Due to PEP 479 the corpusstreamer objects no longer work.
Traceback (most recent call last):
  File "/opt/conda/lib/python3.7/site-packages/vsm/extensions/corpusbuilders/corpusstreamers.py", line 123, in __iter__
    raise StopIteration()
StopIteration

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/opt/conda/bin/topicexplorer", line 11, in <module>
    sys.exit(main())
  File "/opt/conda/lib/python3.7/site-packages/topicexplorer/__main__.py", line 228, in main
    args.config_file = benchmark(init.main)(args)
  File "/opt/conda/lib/python3.7/site-packages/topicexplorer/init.py", line 449, in main
    sentences=args.sentences, tokenizer=args.tokenizer)
  File "/opt/conda/lib/python3.7/site-packages/topicexplorer/init.py", line 370, in build_corpus
    simple=simple, tokenizer=tokenizer)
  File "/opt/conda/lib/python3.7/site-packages/vsm/extensions/corpusbuilders/corpusstreamers.py", line 98, in corpus_from_files
    corpus = corpus_fromlist(corpus, context_type='document', remove_empty=False)
  File "/opt/conda/lib/python3.7/site-packages/vsm/extensions/corpusbuilders/corpusbuilders.py", line 178, in corpus_fromlist
    remove_empty=remove_empty)
  File "/opt/conda/lib/python3.7/site-packages/vsm/corpus/base.py", line 501, in __init__
    words_corpus=words_corpus)
  File "/opt/conda/lib/python3.7/site-packages/vsm/corpus/base.py", line 169, in __init__
    SortedSet(words_corpus if words_corpus else self.corpus), 
  File "/opt/conda/lib/python3.7/site-packages/sortedcontainers/sortedset.py", line 168, in __init__
    self._update(iterable)
  File "/opt/conda/lib/python3.7/site-packages/sortedcontainers/sortedset.py", line 682, in update
    values = set(chain(*iterables))
RuntimeError: generator raised StopIteration
inpho / vsm

StopIteration error in Python 3.7 #168
