text: Title: async is a reserved word
  Body: One of the files is named `async` but this is a reserved word in python 3.7+
  
  ```
  ==================================== ERRORS ====================================
  ___________ ERROR collecting tests/integration/test_async_arctic.py ____________
  ../../../virtualenv/python3.7.1/lib/python3.7/site-packages/_pytest/python.py:450: in _importtestmodule
      mod = self.fspath.pyimport(ensuresyspath=importmode)
  ../../../virtualenv/python3.7.1/lib/python3.7/site-packages/py/_path/local.py:668: in pyimport
      __import__(modname)
  E     File "/home/travis/build/manahl/arctic/tests/integration/test_async_arctic.py", line 1
  E       import arctic.async as aasync
  E                         ^
  E   SyntaxError: invalid syntax
  ```