Hi there, following the example, `pptk.view()` hangs without showing any information. How to reproduce: ```python import numpy as np import pptk x = np.random.rand(100, 3) pptk.viewer(x) ``` I'm running pptk 0.1.0 installed via `pip install --user pptk` with Python 3.7.1 on an x64 Arch Linux machine.