Disk space error with v3 to v4 migration script

I am trying to migrate from v3 to v4 using the provided script (migrate.sh) - https://easyengine.io/handbook/v3-to-v4-migration/script/

However, I am faced with the following error after executing `sudo bash ./migrate.sh --all`:

```
web@xenon:~$ sudo bash migrate.sh --all
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 8214 100 8214 0 0 229k 0 --:--:-- --:--:-- --:--:-- 229k
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 10589 100 10589 0 0 344k 0 --:--:-- --:--:-- --:--:-- 344k
! We require at least 5 GiB disk space free
Disk space is too low to continue migration
```

Here is the output of `df`:

```
web@xenon:~$ df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 981128 0 981128 0% /dev
tmpfs 199208 676 198532 1% /run
/dev/sda1 19626788 3115528 15667240 17% /
tmpfs 996040 0 996040 0% /dev/shm
tmpfs 5120 0 5120 0% /run/lock
tmpfs 996040 0 996040 0% /sys/fs/cgroup
tmpfs 199208 0 199208 0% /run/user/1000
```

I am using Ubuntu 18.04.1 LTS.