LPSE2D tests failing

[jpbrodrick89]

Seems to be a result of #128:

=========================== short test summary info ============================
FAILED tests/test_lpse2d/test_epw_frequency.py::test_epw_frequency[_imaginary_part_] - AssertionError: 
Not equal to tolerance rtol=0.35, atol=0

Mismatched elements: 1 / 1 (100%)
Max absolute difference among violations: 0.00700032
Max relative difference among violations: 0.81848027
 ACTUAL: array(0.001553)
 DESIRED: array(0.008553)