bug when deploy on a sub folder instead of root of a domain

[junnikokuki]

Hi,

I want the deploy leek on a sub folder instead of root of a domain, so I added pathPrefix: '/leek' on gatsby-config.js and made some other modifications needed. But when visit on http://localhost/leek, when redirect to http://localhost/leek/page-data/page-data.json?e3d5d758098a36971ccf1d639dccf5b8?app=leek it became http://localhost/leek/page-data/leek/page-data.json?e3d5d758098a36971ccf1d639dccf5b8?app=leek, it added an unwanted path prefix between page-data and page-data.json. Leek works no problem on 0.5.5 version with my modifications.