There is a typo in docs/install.md

## Problem statement
I think there is a typo in docs/install.md. We have to change it
from

```
go checkout v0.25.0
```

to

```
git checkout v0.25.0
```

source: 
https://github.com/go-swagger/go-swagger/blob/3af79747ddab32ed5bd694514599f06e4299bca4/docs/install.md