Fixed the warnings on package install

The following warnings were being displayed when the package was installed/used:

/usr/lib/go/src/pkg/github.com/codegangsta/cli/context.go:56: function ends without a return statement
/usr/lib/go/src/pkg/github.com/codegangsta/cli/context.go:69: function ends without a return statement
/usr/lib/go/src/pkg/github.com/codegangsta/cli/context.go:78: function ends without a return statement
Merge pull request #21 from andyhmltn/master

Fixed the warnings on package install