php 버전별 업그레이드시 주의사항

1. upgrade 5.2 to 5.3

http://php.net/manual/en/migration53.php

2. upgrade 5.3 to 5.4

http://php.net/manual/en/migration54.php

3. upgrade 5.4 to 5.5

http://php.net/manual/en/migration55.php

4. upgrade 5.5 to 5.6

http://php.net/manual/en/migration56.php

5. upgrade 5.6 to 7.0

http://php.net/manual/en/migration70.php