Skip vendor directory during build when looking for rice files

[markbates]

When running buffalo build with a vendor directory you'll get the following output:

no calls to rice.FindBox() or rice.MustFindBox() found in import path `github.com/gobuffalo/toodo/vendor/github.com/GeertJohan/go.rice`
no calls to rice.FindBox() or rice.MustFindBox() found in import path `github.com/gobuffalo/toodo/vendor/github.com/GeertJohan/go.rice/rice`
no calls to rice.FindBox() or rice.MustFindBox() found in import path `github.com/gobuffalo/toodo/vendor/github.com/gobuffalo/buffalo/buffalo/cmd`

The build works just fine, but there's no reason to even look in the vendor directory.