temporarily pin cffi to avoid bug related to virtualenv (#4083)

* temporarily pin cffi to avoid bug related to virtualenv

* right, don't duplicate the name
diff --git a/setup.py b/setup.py
index 9250e2d..800e94d 100644
--- a/setup.py
+++ b/setup.py
@@ -52,7 +52,7 @@
             "upgrade PyPy to use this library."
         )
 else:
-    setup_requirements.append("cffi>=1.7")
+    setup_requirements.append("cffi>=1.7,!=1.11.3")
 
 test_requirements = [
     "pytest>=3.2.1,!=3.3.0",