Update modelzoo.ipynb

fixes: tensorflow#236

notebooks/modelzoo.ipynb

@@ -38,9 +38,12 @@
    "source": [
     "# Expanded modelzoo is only available as of lucid v0.3\n",
     "!pip install --quiet lucid==0.3\n",
+    "#tensorflow_version only works in colab\n",
+    "%tensorflow_version 1.x\n",
     "\n",
     "import numpy as np\n",
     "import tensorflow as tf\n",
+    "assert tf.__version__.startswith('1')\n",
     "\n",
     "from lucid.misc.io import show, load\n",
     "import lucid.optvis.objectives as objectives\n",
@@ -459,4 +462,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 1
-}
+}