test: raise the allocation threshold for chan/select2.go failure

Updates #5282

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/8718045

test/chan/select2.go

@@ -47,7 +47,7 @@ func main() {
 	runtime.GC()
 	runtime.ReadMemStats(memstats)
 
-	if memstats.Alloc-alloc > 1e5 {
+	if memstats.Alloc-alloc > 1.1e5 {
 		println("BUG: too much memory for 100,000 selects:", memstats.Alloc-alloc)
 	}
 }