Exclude known-broken pyparsing versions

We ran into the following pyparsing bug:
pyparsing/pyparsing#345

After some bisecting it turned out it's only present in pyparsing 3.0.5-6,
and the pyparsing folks were quick to fix it for 3.0.7.

Exclude the broken versions from install_requires.

setup.py

@@ -35,7 +35,7 @@ def get_version():
     ],
     platforms=['any'],
     install_requires=[
-        'pyparsing>=2.0.0',
+        'pyparsing >=2.0.0, !=3.0.5, !=3.0.6',
     ],
     classifiers=[
         'Development Status :: 3 - Alpha',