Backporting the changes made in #139 (#140)

* Backporting the changes made in https://github.com/egulias/EmailValidator/pull/139 so this functionality is also accessible in the 1.2.x releases.
This fix allows for more compliance with the DNS RFC. Explanation here: https://github.com/egulias/EmailValidator/pull/139/commits/08bac068c26edd210daa259a2819d7dfd7438091

src/Egulias/EmailValidator/EmailValidator.php

@@ -184,7 +184,10 @@ class EmailValidator implements EmailValidatorInterface
      */
     protected function checkDNS()
     {
-        $mxRecordExists = checkdnsrr(trim($this->parser->getParsedDomainPart()), 'MX');
+        $host = $this->parser->getParsedDomainPart();
+        $host = rtrim($host, '.') . '.';
+
+        $mxRecordExists = checkdnsrr($host, 'MX');
 
         if (!$mxRecordExists) {
             $this->warnings[] = self::DNSWARN_NO_RECORD;