Update get_cmap syntax and set minimum matplotlib version

Author: kburns

dedalus/extras/plot_tools.py

@@ -119,7 +119,7 @@ def plot_bot(dset, image_axes, data_slices, image_scales=(0,0), clim=None, even_
         axes.axis('off')
 
     # Colormap options
-    cmap = copy.copy(matplotlib.cm.get_cmap(cmap))
+    cmap = plt.get_cmap(cmap)
     cmap.set_bad('0.7')
 
     # Plot

setup.py

@@ -183,7 +183,7 @@ def read(rel_path):
 install_requires = [
     "docopt",
     "h5py >= 3.0.0",
-    "matplotlib",
+    "matplotlib >= 3.7.0",
     "mpi4py >= 2.0.0",
     "numexpr",
     "numpy >= 1.20.0",