Typing wrongly in hypatia/satviz/scripts/visualize_constellation.py

On the line of 251, `viz_string = generate_satellite_trajectories()` is typed wrongly as `viz_string = generate_satelite_trajectories()`, which will make error:
```
Traceback (most recent call last):
  File "visualize_constellation.py", line 251, in <module>
    viz_string = generate_satelite_trajectories()
NameError: name 'generate_satelite_trajectories' is not defined
```
