Missing gc_type tag for gc.pause.by.type metrics

[jfirebaugh]

The runtime.node.gc.pause.by.type.* metrics are intended to include a gc_type tag:

dd-trace-js/packages/dd-trace/src/platform/node/metrics.js

Line 226 in 68b93df

histogram('gc.pause.by.type', stats.gc[type], { gc_type: type })

However, the histogram function ignores the third parameter, so post-aggregation, these metrics aren't really meaningful:

dd-trace-js/packages/dd-trace/src/platform/node/metrics.js

Lines 255 to 263 in 68b93df

	function histogram (name, stats) {
	client.gauge(`${name}.min`, stats.min)
	client.gauge(`${name}.max`, stats.max)
	client.increment(`${name}.sum`, stats.sum)
	client.gauge(`${name}.avg`, stats.avg)
	client.increment(`${name}.count`, stats.count)
	client.gauge(`${name}.median`, stats.median)
	client.gauge(`${name}.95percentile`, stats.p95)
	}