fix go 1.15 errors (#5277)

## Description

fix golang 1.15 errors. 

Closes: #XXX

libs/cmap/cmap_test.go

@@ -60,10 +60,10 @@ func TestContains(t *testing.T) {
 func BenchmarkCMapHas(b *testing.B) {
 	m := NewCMap()
 	for i := 0; i < 1000; i++ {
-		m.Set(string(i), i)
+		m.Set(string(rune(i)), i)
 	}
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		m.Has(string(i))
+		m.Has(string(rune(i)))
 	}
 }

libs/pubsub/pubsub_test.go

@@ -444,7 +444,7 @@ func benchmarkNClients(n int, b *testing.B) {
 		err = s.PublishWithEvents(
 			ctx,
 			"Gamora",
-			map[string][]string{"abci.Account.Owner": {"Ivan"}, "abci.Invoices.Number": {string(i)}},
+			map[string][]string{"abci.Account.Owner": {"Ivan"}, "abci.Invoices.Number": {string(rune(i))}},
 		)
 		require.NoError(b, err)
 	}

p2p/upnp/upnp.go

@@ -209,7 +209,7 @@ func getServiceURL(rootURL string) (url, urnDomain string, err error) {
 	defer r.Body.Close()
 
 	if r.StatusCode >= 400 {
-		err = errors.New(string(r.StatusCode))
+		err = errors.New(string(rune(r.StatusCode)))
 		return
 	}
 	var root Root