Set the test_suite variable to avoid TypeError in setuptools

setup.py

@@ -84,9 +84,12 @@ tests_require = [
 
 
 class PyTest(TestCommand):
+    def initialize_options(self):
+        TestCommand.initialize_options(self)
+        self.test_suite = 'tests'
+
     def finalize_options(self):
         TestCommand.finalize_options(self)
-        self.test_suite = True
 
     def run_tests(self):
         #import here, cause outside the eggs aren't loaded