test: replace string concatenation with template

test: replace string concatenation with template · nodejs/node@4243903

Original file line number	Diff line number	Diff line change
`@@ -39,9 +39,10 @@ const server = http.createServer(common.mustCall(function(req, res) {`
`39`	`39`
`40`	`40`	`// Make a bunch of requests pipelined on the same socket`
`41`	`41`	`function generator(seeds) {`
	`42`	`+const port = server.address().port;`
`42`	`43`	`return seeds.map(function(r) {`
`43`		`-return 'GET /' + r + ' HTTP/1.1\r\n' +`
`44`		-`Host: localhost:${server.address().port}\r\n` +
	`44`	+return `GET /${r} HTTP/1.1\r\n` +
	`45`	+`Host: localhost:${port}\r\n` +
`45`	`46`	`'\r\n' +`
`46`	`47`	`'\r\n';`
`47`	`48`	`}).join('');`