Fix export to custom paths

[kick-the-bucket]

Strangely the trailing slash is only appended to $rootDir if one provides an export-path option.
This results in double-slashes in $outputPath, which in turn results in is_dir($outputPath) returning false, even if the directory actually exists and mkdir failing, because of undetected existing directory.

[gilles-g]

Hi,
What is your environment for test? Windows, linux?

[kick-the-bucket]

Linux. But I think the double slash in the custom built path should break things in any environment...