Simply add the following code after [opcache] in /etc/php/7.0/fpm/php.ini
opcache.enable=1
opcache.enable_cli=0
opcache.memory_consumption=256
opcache.interned_strings_buffer=4
opcache.max_accelerated_files=20000
opcache.max_wasted_percentage=5
opcache.validate_timestamps=1
opcache.revalidate_freq=2
opcache.optimization_level=0xffffffff
