Add typing to dependencies

[natruiz3555]

After installing this module (version 0.5.0) from PyPI on Debian Stretch, I got the following error:

>>> import greenstalk
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/user/programming/queue-test/venv/lib/python3.4/site-packages/greenstalk.py", line 2, in <module>
    from typing import Any, BinaryIO, Dict, Iterable, List, Optional, Tuple, Union
ImportError: No module named 'typing'

After installing the typing module (at version 3.6.1) it worked fine.

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master     #3   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines         161    161           
=====================================
  Hits          161    161

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[natruiz3555]

Oops, I was running Debian Jessie with Python 3.4.2...