fix code length

pages/register.vue

@@ -200,7 +200,7 @@
           this.$refs.identifyCode.focus();
           return false;
         }
-        if(this.identifyCode.length !== 4){
+        if(this.identifyCode.length !== 6){
           this.$message({
             showClose: true,
             message: '验证码长度错误',