Reorder envs and include doc in travis

tox.ini

 [tox]
 skip_missing_interpreters = True
-envlist = clean, lint, py35, py36, inst, setup, unit, integration, stats
+envlist = py35, py36, inst, setup, unit, integration, lint, stats, doc, clean
 
 [travis]
 python =
-    3.5: lint, py35, inst, setup, unit, integration
+    3.5: py35, inst, setup, unit, integration, lint, doc
     3.6: py36, inst, setup, unit, integration
 
 [testenv]