Open /etc/default/grub and edit the line

GRUB_CMDLINE_LINXU_DEFAULT="quiet spash"

to read

GRUB_CMDLINE_LINXU_DEFAULT="quiet spash resume=/dev/mapper/mint--vg-swap_1"

where the latter part should be edited to point to your swap partition, which must be at least as large as your RAM.

Afterwards, run:

sudo update-grub2