add pypy3.5 to our test matrix (#3709)

* add pypy3.5 to our test matrix

* pypy-nocoverage time
diff --git a/.travis.yml b/.travis.yml
index f84b419..5bfe15b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -33,6 +33,7 @@
           env: TOXENV=py36
         - env: TOXENV=pypy PYPY_VERSION=pypy2-5.3
         - env: TOXENV=pypy PYPY_VERSION=pypy2.7-5.8.0
+        - env: TOXENV=pypy-nocoverage PYPY_VERSION=pypy3.5-5.8.0
         - python: 2.7
           env: TOXENV=py27 OPENSSL=1.1.0f
         - python: 3.5
@@ -72,7 +73,7 @@
         - language: generic
           os: osx
           osx_image: xcode8.3
-          env: TOXENV=pypy CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS=1 PYPY_VERSION=pypy2.7-5.8.0
+          env: TOXENV=pypy-nocoverage CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS=1 PYPY_VERSION=pypy2.7-5.8.0
         - language: generic
           os: osx
           osx_image: xcode8.3
diff --git a/tox.ini b/tox.ini
index 525ffe2..89bcaae 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,6 +18,14 @@
     coverage combine
     coverage report -m
 
+# This target disables coverage on pypy because of performance problems with
+# coverage.py on pypy.
+[testenv:pypy-nocoverage]
+basepython = pypy
+commands =
+    pip list
+    pytest --capture=no --strict {posargs}
+
 [testenv:docs]
 extras =
     docstest