Merge pull request certbot#3496 from certbot/cffix

Fixes cffi errors in Travis during oldest tests

Author: bmw

tox.ini

@@ -29,13 +29,16 @@ setenv =
     PYTHONHASHSEED = 0
 # https://testrun.org/tox/latest/example/basic.html#special-handling-of-pythonhas
 
+# cffi<=1.7 is required for oldest tests due to
+# https://bitbucket.org/cffi/cffi/commits/18cdf37d6b2691301a15b0e54f49757ebd4ed0f2?at=default
 deps =
+    py{26,27}-oldest: cffi<=1.7
     py{26,27}-oldest: cryptography==0.8
     py{26,27}-oldest: configargparse==0.10.0
+    py{26,27}-oldest: dnspython>=1.12
     py{26,27}-oldest: psutil==2.1.0
     py{26,27}-oldest: PyOpenSSL==0.13
     py{26,27}-oldest: python2-pythondialog==3.2.2rc1
-    py{26,27}-oldest: dnspython>=1.12
 
 [testenv:py33]
 commands =