- fix a flaky test on py35-xdist by calling

importlib.invalidate_caches()

- bump version to 2.8.1

- regen docs

- amend changelog, authors

doc/en/tmpdir.rst

@@ -29,7 +29,7 @@ Running this would result in a passed test except for the last
 
     $ py.test test_tmpdir.py
     ======= test session starts ========
-    platform linux -- Python 3.4.2, pytest-2.8.1.dev1, py-1.4.30, pluggy-0.3.1
+    platform linux -- Python 3.4.3, pytest-2.8.1, py-1.4.30, pluggy-0.3.1
     rootdir: $REGENDOC_TMPDIR, inifile: 
     collected 1 items