Edit the file
/etc/default/rcS with your favorite text editor, ie:
sudo nano /etc/default/rcS
Look for the UTC=foo (yes/no) line and change it to UTC=yes.
rcS(5) man page:
This is used to govern how the hardware real time clock is interpreted when it is read (e.g., at boot time, for the purpose of setting the system clock) and when it is written (e.g., at shutdown). If this option is set to no then the system clock is
assumed to be set to local time. If the option is set to yes then the system clock is assumed to be set to something approximating Coordinated Universal Time (UTC). (POSIX systems keep a variant of UTC, without leap seconds.)