Fix for getRefreshToken() in Pdo.php

Fix for 'PDOStatement::execute() expects parameter 1 to be array, string
given' introduced by line 148 in commit
97bdd2ca13ae03415982cdab8965dc605b4882be
Fix for expireAuthorizationCode() in Pdo.php

Fix for 'PDOException' with message 'SQLSTATE[HY093]: Invalid parameter
number: parameter was not defined' introduced in commit
42e626cce684e6aa9a64bfc94f6e4b9dc4a837cf
Merge pull request #37 from dsquier/develop

Fix for getRefreshToken() in Pdo.php