Force HTTP check under corresponding protocols

[solarispika]

Fixes #55.

Since URL object with http or https protocol and default port(80 or 443)
will not show the port, the port is only assigned to default port 443
when the protocol is neither one of them.

[sindresorhus]

CI is failing

[solarispika]

The failed test tests imap.gmail.com:995 which is prepended with http:// before testing.
I see comment on target says: Protocols other than http: and https: are not supported.
I'm not sure if the test have its purpose or it can be removed?
Or maybe we can only force HTTP check when the target is explicitly using HTTP?

[sindresorhus]

This is overly complicated.

Suggested change

	const isHTTP = ['http:', 'https:'].some(prot => target.indexOf(prot) === 0);
	const isHTTP = target.startsWith('https://') || target.startsWith('http://');

[sindresorhus]

Or maybe we can only force HTTP check when the target is explicitly using HTTP?

Isn't that what we are already doing now?

[sindresorhus]

I'm not sure if the test have its purpose or it can be removed?

I would recommend "git blaming" it and check why it was added.

[solarispika]

#38 removed support for other well-known protocol, so it changed the test of ftp url to the current one.
The words "Protocols other than http: and https: are not supported." does not limit the use of other ports.
I think it is fine to leave the test now.