[BUG] Sort should be numeric

**Sort should be numeric instead of alphabetic**

when sorting by memory, threads or CPU 15 comes after 2 because (apparently) it uses alphabetic sorting.

**To Reproduce**

This happens if you have a number that comes alphabetically before but has a higher absolute value than other. (e.g. 15 and 2 or 25 and three).

**Expected behavior**

should behave like coreutils `sort -n` (numeric sort)

**Screenshots**


**Info (please complete the following information):**
- Bashtop version: 0.9.25
- (Linux) Linux distribution and version: Ubuntu 18.04 updated
- Terminal used: Konsole
- Font used: Hack NerdFont Regular
- Bash version, `bash --version` (version 4.4 or above is required): 4.4.20
- Locales: output of `locale -v`
```
LANG=C.UTF-8
LANGUAGE=
LC_CTYPE="C.UTF-8"
LC_NUMERIC=C.UTF-8
LC_TIME=C.UTF-8
LC_COLLATE="C.UTF-8"
LC_MONETARY=C.UTF-8
LC_MESSAGES="C.UTF-8"
LC_PAPER=C.UTF-8
LC_NAME=C.UTF-8
LC_ADDRESS=C.UTF-8
LC_TELEPHONE=C.UTF-8
LC_MEASUREMENT=C.UTF-8
LC_IDENTIFICATION=C.UTF-8
LC_ALL=
```

**Additional context**

contents of `$HOME/.config/bashtop/error.log`
```
New instance of bashtop version: 0.9.25 Pid: 5478
PSUTIL ERROR! Command: get_disks(exclude='squashfs')
not sure how to interpret line ' 7 0 loop0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0\n'
```