Fixes #116. Numpy 1.16 no longer allows changing WRITABLE flag on an array. Copy cast to return a modifiable array from GXvv._get_data_np.
Fixes #116. Numpy 1.16 no longer allows changing WRITABLE flag on an array. Copy cast to return a modifiable array from GXvv._get_data_np.

GeosoftInc/gxpy