tox: Downgrade pyparsing to 2.1.1

It seems pyparsing 2.1.2 is broken with Python 3.4:

    >>> import pyparsing
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File ".../pyparsing.py", line 3478, in <module>
        _escapedPunc = Word( _bslash, r"\[]-*.$+^?()~ ", exact=2 ).setParseAction(lambda s,l,t:t[0][1])
      File ".../pyparsing.py", line 948, in setParseAction
        self.parseAction = list(map(_trim_arity, list(fns)))
      File ".../pyparsing.py", line 808, in _trim_arity
        this_line = extract_stack()[-1]
      File ".../pyparsing.py", line 793, in extract_stack
        return [(frame_summary.filename, frame_summary.lineno)]
    AttributeError: 'tuple' object has no attribute 'filename'

That breaks flake8-putty and thus flake8.
See https://sourceforge.net/p/pyparsing/bugs/95/

tox.ini

@@ -168,7 +168,7 @@ deps =
     pep8-naming==0.3.3
     pydocstyle==1.0.0
     pyflakes==1.2.2
-    pyparsing==2.1.2
+    pyparsing==2.1.1  # rq.filter: != 2.1.2
     six==1.10.0
     sortedcontainers==1.4.4
     venusian==1.0