bug: support array argument to labels() again

This was undocumented and untested, and broke in 13.1.0.

Fixes #499

README.md

@@ -315,6 +315,8 @@ gauge.set({ method: 'GET', statusCode: '200' }, 100);
 gauge.labels({ method: 'GET', statusCode: '200' }).set(100);
 // 3rd version: And again the same effect as above
 gauge.labels('GET', '200').set(100);
+// 4th version: And again the same effect as above
+gauge.labels(['GET', '200']).set(100);
 ```
 
 It is also possible to use timers with labels, both before and after the timer

lib/util.js

@@ -44,7 +44,7 @@ exports.setValueDelta = function setValueDelta(
 };
 
 exports.getLabels = function (labelNames, args) {
-	if (typeof args[0] === 'object') {
+	if (typeof args[0] === 'object' && !Array.isArray(args[0])) {
 		return args[0];
 	}
 

test/gaugeTest.js

@@ -162,6 +162,13 @@ describe.each([
 				it('should handle labels provided as an object', async () => {
 					instance.labels({ code: '200' }).inc();
 
+					const values = (await instance.get()).values;
+					expect(values).toHaveLength(1);
+					expect(values[0].labels).toEqual({ code: '200' });
+				});
+				it('should handle labels provided as an array', async () => {
+					instance.labels([200]).inc();
+
 					const values = (await instance.get()).values;
 					expect(values).toHaveLength(1);
 					expect(values[0].labels).toEqual({ code: '200' });