net/http: adjust a substring which matches "uninteresting" goroutine.

This change allows the check to pass unmodified under GopherJS, which
stack traces are formatted differently (due to being generated by
NodeJS). There are no other functions named `interestingGoroutines` in
the standard library, so it's very unlikely to create false negatives,
and will allow reduce the number of overlays GopherJS needs to maintain.

src/net/http/main_test.go

@@ -43,7 +43,7 @@ func interestingGoroutines() (gs []string) {
 			// These only show up with GOTRACEBACK=2; Issue 5005 (comment 28)
 			strings.Contains(stack, "runtime.goexit") ||
 			strings.Contains(stack, "created by runtime.gc") ||
-			strings.Contains(stack, "net/http_test.interestingGoroutines") ||
+			strings.Contains(stack, "interestingGoroutines") ||
 			strings.Contains(stack, "runtime.MHeap_Scavenger") {
 			continue
 		}