The "uptime" cmd from the default config is not working

## What's broken?
The [uptime](https://github.com/wtfutil/wtf/blob/edad1b155d729dbafeb5dcdfca864a52d8151c62/cfg/default_config_file.go#L95)  cmd is not working properly, it is showing `exit status 1` 

But it works if I remove the empty string `""` from the args:
```
args: [""]
cmd: "uptime"
```
Args without `""`
```
args: []
cmd: "uptime"
```
