Note that the path element has a hyphen for jquery-sparkline. In your example you put a "." - to be fair, so did I at first! Hope that solves your issue.
This didn’t work for me. I took a step back and added moments successfully. Aurelia.json changes are not required.
After a bit of investigation I found out that even though import {} from 'jquery.sparkline' might be the correct statement the script was not being loaded as the script was not referenced in the code. If its not referenced, webpack won’t load it . for example,
import * as moment from 'moment';
...
console.log("The time is " + moment());
...
Moment.js will load because its referenced. However, with sparkline, the plugin is injected into jQuery and webpack has no way of knowing that $(this.elm).sparkline() refers to the jQuery.sparkline plugin.
So what I did (in sparkling.ts) was change the import to require('../../../node_modules/jquery.sparkline/jquery.sparkline');
As a result, the component works as expected.
The only thing is that I am not happy with providing the full path to the script file. Does anyone have a solution for this?