Some plots not possible for single parameter

[stemasc]

Quick fixes:

To calibration_ecdf.py add in line 157:
if not isinstance(plot_data["axes"], np.ndarray):
plot_data["axes"] = np.array([plot_data["axes"]])

To plot_utils.py add:

if not isinstance(axes, np.ndarray):
axes = np.array([axes])

in:

1. prettify_subplots
2. add_x_labels
3. add_y_labels
   respectively at the beginning of the function

[paul-buerkner]

Thank you! Would you mind making a small PR?

[han-ol]

Thanks for bringing this up! The PR #303 should fix the issue.