fix(notebook): convert array index to int

since py3 division return float

fix error:

IndexError: only integers, slices (`:`), ellipsis (`...`), numpy.newaxis
(`None`) and integer or boolean arrays are valid indices

dct_better_explained.ipynb

@@ -249,7 +249,7 @@
     "fig = plt.figure(figsize=(16, 16))\n",
     "for ii in range(img_h*img_h):\n",
     "    plt.subplot(8, 8, ii + 1)\n",
-    "    plt.title(partial_z_dct[ii][ii / 8, ii % 8])\n",
+    "    plt.title(partial_z_dct[ii][int(ii / 8), ii % 8])\n",
     "    plt.imshow(partial_z_idct[ii], cmap='gray', interpolation='nearest')\n",
     "    plt.grid(False);\n",
     "    plt.xticks([]);\n",