fix tests

setup.py

@@ -7,6 +7,7 @@ from setuptools import setup, find_packages
 from setuptools.command.test import test as TestCommand
 
 import httpie
+from httpie.compat import is_py27
 
 
 class PyTest(TestCommand):
@@ -33,6 +34,9 @@ tests_require = [
     'mock',
 ]
 
+if is_py27:
+    tests_require.append('pyOpenSSL')
+
 
 install_requires = [
     'requests>=2.21.0',