fix: fix broken link in covid notebook (#450)

* fix: fix broken link in covid notebook

* Update bq_dataframes_covid_line_graphs.ipynb

---------

Co-authored-by: Henry J Solberg <henryjsolberg@google.com>

Author: milkshakeiii

notebooks/visualization/bq_dataframes_covid_line_graphs.ipynb

@@ -34,7 +34,7 @@
         "<table align=\"left\">\n",
         "\n",
         "  <td>\n",
-        "    <a href=\"https://colab.research.google.com/github/googleapis/python-bigquery-dataframes/tree/main/notebooks/dataframes/bq_dataframes_covid_line_graphs.ipynb\">\n",
+        "    <a href=\"https://colab.research.google.com/github/googleapis/python-bigquery-dataframes/blob/main/notebooks/visualization/bq_dataframes_covid_line_graphs.ipynb\">\n",
         "      <img src=\"https://cloud.google.com/ml-engine/images/colab-logo-32px.png\" alt=\"Colab logo\"> Run in Colab\n",
         "    </a>\n",
         "  </td>\n",