feat(cmd): use tabwritter to line things up

So pretty

```
UNIT			LOAD	ACTIVE	SUB	DESC	MACHINE
web@8000.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
web@8001.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
web@8002.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
```
Merge pull request #20 from philips/pretty-tabs

feat(cmd): use tabwritter to line things up