Change Tilda API URL to https

[fervallen]

Tilda API has a hardcoded API URL in this file:

tilda-php/src/TildaApi.php

Line 25 in 366508c

protected $endpoint = 'http://api.tildacdn.info/v1';

Now Tilda added a 301 redirect from http to https.
By default CURL does not follow 301 redirect in many systems and any requests to API now resulting with Invalid JSON Exception.

[mxl]

@fervallen Could you prepare PR?