Specify a minimum six version requirement.

jmchilton · jmchilton · commit 1c7ee5b45921 · 2015-11-19T12:19:50.000Z
Fixes #376, thanks @peterjc.
diff --git a/requirements.txt b/requirements.txt
@@ -1,5 +1,5 @@
 Click
-six
+six>=1.7.0
 pyyaml
 bioblend
 docutils
diff --git a/setup.py b/setup.py
@@ -16,7 +16,7 @@
 
 requirements = [
     'Click',
-    'six',
+    'six>=1.7.0',
     'pyyaml',
     'jinja2',
     'docutils',
