improve example codes

.example/encoding/ghash/ghash_repeat_check.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/gogf/gf/encoding/ghash"
+)
+
+func main() {
+	m := make(map[uint64]bool)
+	for i := 0; i < 100000000; i++ {
+		hash := ghash.BKDRHash64([]byte("key_" + strconv.Itoa(i)))
+		if _, ok := m[hash]; ok {
+			fmt.Printf("duplicated hash %d\n", hash)
+		} else {
+			m[hash] = true
+		}
+	}
+}