When upgrading wordpress to newer release, sometimes it may come out following error:
Download failed.: SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
Some fixes on web forum suggest to edit curl config in php.ini file. It can be fixed quickly without touching this system level configuration. It can be fixed by editing your CURRENT theme file.
Add following codes to theme