fix broken link causing tests to fail

Author: HuwCheston

mirdotcom/content/2_music_representations/sheet_music_representations.ipynb

@@ -204,7 +204,7 @@
    },
    "source": [
     "ipd.Image(\n",
-    "    url=\"https://upload.wikimedia.org/wikipedia/commons/thumb/9/98/Pitch_class_on_C.png/187px-Pitch_class_on_C.png\"\n",
+    "    url=\"https://upload.wikimedia.org/wikipedia/commons/0/03/Middle_C.png\"\n",
     ")"
    ],
    "outputs": [