Fix package selection in setup.py (#758)

Author: biniow

setup.py

@@ -31,7 +31,7 @@ def find_stubs(package):
 setup(
     name='pynamodb',
     version=__import__('pynamodb').__version__,
-    packages=find_packages(exclude=('tests',)),
+    packages=find_packages(exclude=('tests', 'tests.integration',)),
     url='http://jlafon.io/pynamodb.html',
     author='Jharrod LaFon',
     author_email='jlafon@eyesopen.com',