Fix gates.ipynb formatting (quantumlib#5175)

- Move import cirq up into top block.
- Clear outputs.

docs/gates.ipynb

@@ -75,7 +75,8 @@
     "except ImportError:\n",
     "    print(\"installing cirq...\")\n",
     "    !pip install --quiet cirq\n",
-    "    print(\"installed cirq.\")"
+    "    print(\"installed cirq.\")\n",
+    "    import cirq"
    ]
   },
   {
@@ -128,22 +129,8 @@
    "metadata": {
     "id": "psYGZcjUEF5V"
    },
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "H(b)\n",
-      "CNOT(b, c)\n",
-      "CNOT(a, b)\n",
-      "H(a)\n",
-      "cirq.MeasurementGate(2, 'a,b', ())(a, b)\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
-    "import cirq\n",
-    "\n",
     "# This examples uses named qubits to remain abstract.\n",
     "# However, we can also use LineQubits or GridQubits to specify a geometry\n",
     "a = cirq.NamedQubit('a')\n",
@@ -354,9 +341,7 @@
  ],
  "metadata": {
   "colab": {
-   "collapsed_sections": [
-    "Sh9QBnKbFf_B"
-   ],
+   "collapsed_sections": [],
    "name": "gates.ipynb",
    "toc_visible": true
   },