Stop pinning lz4

Opening a PR to check if tests pass with the new version. If so, we'll want to bump `requirements-dev.txt` as well.

Many thanks to @jonathanunderwood for his diligent work here: #1021 (comment)

Author: jeffwidman

tox.ini

@@ -18,7 +18,7 @@ deps =
     pytest-mock
     mock
     python-snappy
-    lz4==0.11.1
+    lz4
     xxhash
     py26: unittest2
 commands =