Replaced `c_in` with `in_channels`

as proposed in [Better example code? #13](https://huggingface.co/stabilityai/stable-cascade/discussions/13#65ce2b43be38705ceecdd4bc) by

@fischpferd

.

prior/config.json

@@ -32,7 +32,7 @@
     2048,
     2048
   ],
-  "c_in": 16,
+  "in_channels": 16,
   "c_out": 16,
   "c_pixels": null,
   "c_r": 64,