Fix Codemirror CSS path
Fix Codemirror CSS path

change dead link https://codemirror.net/lib/codemirror.css
to https://codemirror.net/5/lib/codemirror.css
GoogleCloudPlatform/bigquery-geo-viz,GoogleCloudPlatform/bigquery-geo-viz,GoogleCloudPlatform/bigquery-geo-viz