Joi.string().uri() fails to validate uri with 2 #, but new URL() works

#### Support plan

* *is this issue currently blocking your project?* (yes/no): Yes
* *is this issue affecting a production system?* (yes/no): No

#### Context

* *node version*: 12
* *module version with issue*: 17.1.1
* *environment* (e.g. node, browser, native): node

Related: https://github.com/facebook/docusaurus/issues/3219

#### What are you trying to achieve or the steps to reproduce?

Code sandbox: https://codesandbox.io/s/joi-validation-interactive-52stl?file=/src/index.js:292-386

```js
Joi.string()
.uri()
.validate("https://riot.im/app/#/room/#ligo-public:matrix.org")
```

#### What was the result you got?

```
console.log(
Joi.string()
.uri()
.validate("https://riot.im/app/#/room/#ligo-public:matrix.org"),
);

console.log(new URL("https://riot.im/app/#/room/#ligo-public:matrix.org"));
```

Joi returns an error, while the URL is parseable

#### What result did you expect?

Joi does not return an error