Changing versions breaks url_base property in ActiveCampaign class

[RonanBitpuma]

The piece of code causing the issue:

activecampaign-api-php/includes/ActiveCampaign.class.php

Lines 78 to 83 in 2bf5b72

	function version($version) {
	$this->version = (int)$version;
	if ($version == 2) {
	$this->url_base = $this->url_base . "/2";
	}
	}

This is what I do:

What I did to reproduce the bug

1. I get the contact list
2. This does not work, which is correct, as I haven't set the version
3. I set the version to 2
4. I get the contact list
5. This works, as intended.
6. I set the version back to 1, this is where the $url_base property 'breaks'
7. I get the contact list
8. This does not work, which is correct, as the version is back to 1
9. I set the version back to 2
10. I get the contact list
11. This does not work, while it should. $ac->url_base now returns api_url.com/2/2 (Note the double /2!)

Because of this bug it requires me to create new instances of the ActiveCampaign class, instead of using one single instance