That does not look like the correct syntax for changing a seriesStyle in orde to make it a line chart. You can use the samples from here to help you:
That is possible but you would need to change the shape of your data. Here's an example of one (slightly hacky) way to achieve this in Canvas without changing your Elasticsearch index.
The color arg in pointseries splits a column into multiple series per unique value in a single column. There currently isn't a way to assign a series to a specific column in Canvas. So ideally, your data would be in a shape like this:
{ "timestamp": "2019-05-01 00:00:00", "count_type": "active", "count": 176 }
{…
Looks like you would have to change it to something more similar to this:
| plot
defaultStyle={seriesStyle lines=1 fill=1}