gstlal tests raise SyntaxError on python3.6

The gstlal/tests/test_common.py script raises a SyntaxError on python3.6:

$ python3.6 tests/test_common.py
  File "tests/test_common.py", line 148
    def need_data(elem, arg, (input_arrays, rate)):
                             ^
SyntaxError: invalid syntax