Fix for RELEASES URLs not containing the app name when using Nuts as an Express middleware

[biw]

When search parameters are present in the URL that Electron sends to Nuts:
For example:
http://localhost:4000/myApp/update/win32/1.0.0/RELEASES?arch=amd64

The app name is being omitted:
http://localhost:4000/download/1.1.0/my-app-1.1.0-full.nupkg

Expected Result:
http://localhost:4000/myApp/download/1.1.0/my-app-1.1.0-full.nupkg

resolves #150

From GitbookIO/nuts#159