Metric expressjs_number_of_open_connections does not include prefix

[kennsippell]

const prometheusMiddleware = require('prometheus-api-metrics');
app.use(prometheusMiddleware({
  metricsPrefix: 'prefix',
}));

expressjs_number_of_open_connections should be prefix_expressjs_number_of_open_connections but it appears to be the only metric without the prefix