Fix base port in ipynb example (#3283)

notebooks/getting-started.ipynb

    "outputs": [],
    "source": [
     "engine_configuration_channel = EngineConfigurationChannel()\n",
-    "env = UnityEnvironment(base_port = 5006, file_name=env_name, side_channels = [engine_configuration_channel])\n",
+    "env = UnityEnvironment(base_port = 5004, file_name=env_name, side_channels = [engine_configuration_channel])\n",
     "\n",
     "#Reset the environment\n",
     "env.reset()\n",