can't uninstall by using a branch or a commit hash

when using these command:
```
  pgvm uninstall master
  pgvm uninstall 86ef479
```
display usage.
```
~$ pgvm uninstall master

Usage: pgvm uninstall <version> [OPTIONS]

  <version> is the postgres semantic version that
            you want to uninstall.

  Examples:
           pgvm uninstall 9.0.7
           pgvm uninstall 9.1.3
           pgvm uninstall 9.1.1 --purge
           pgvm uninstall --all
           pgvm uninstall --all --purge
           pgvm uninstall master


== Options


  --all		Remove all postgres versions installed.

  --purge	Remove postgres version source.

  --force	If is the current version then remove it.
```