Fix bug preventing update from working

This bug didnt fetch tags with git, so nothing would ever update.

To upgrade to this version if you are experiencing this issue do the following:

pushd ~/.chefvm
git fetch --tags origin
popd
chefvm update

Then you should be on the latest, confirm this by running chefvm version and you should see "1.3.1"

Add Support for export and import

This adds the ability to export configurations and import them into another chefvm install.

Added support for Fish shell

This should enable chefvm to be used in fish shell.

Tab complete config names also

Thanks to @bookest you can now do the following (assuming you have a config name myconfig):

$ chefvm my[TAB]

will complete to:

$ chefvm myconfig

Minor fixes

Minor fixes for exit status by @pdf