Add support for Python 2.6 in docs conf

docs/conf.py

@@ -5,6 +5,9 @@ import os
 import sys
 import subprocess
 
+if 'check_output' not in dir(subprocess):
+	import subprocess32 as subprocess
+
 extensions = [
     'sphinx.ext.autodoc',
     'rst.linker',

tests/requirements.txt

@@ -1 +1,2 @@
 pytest >= 2.8
+subprocess32; python_version=="2.6"