allow single-param plot with np.atleast_2d(axes)

gridcorner.py

@@ -56,6 +56,7 @@ def _get_fig_and_axes(ndim, factor, whspace):
     plotdim = factor * ndim + factor * (ndim - 1.) * whspace
     dim = lbdim + plotdim + trdim
     fig, axes = plt.subplots(ndim, ndim, figsize=(dim, dim))
+    axes = np.atleast_2d(axes) # allow single-parameter plots
 
     # Format the figure.
     lb = lbdim / dim