Update library version number.

Author: ruscoe

src/Mailchimp.php

@@ -14,7 +14,7 @@
  */
 class Mailchimp implements MailchimpApiInterface {
 
-  const VERSION = '2.0.0';
+  const VERSION = '3.0.0-rc6';
   const DEFAULT_DATA_CENTER = 'us1';
 
   const ERROR_CODE_BAD_REQUEST = 'BadRequest';

src/Mailchimp2.php

@@ -14,7 +14,7 @@
  */
 class Mailchimp2 implements MailchimpApiInterface {
 
-  const VERSION = '2.0.0';
+  const VERSION = '3.0.0-rc6';
   const DEFAULT_DATA_CENTER = 'us1';
 
   const ERROR_CODE_BAD_REQUEST = 'BadRequest';