Having problem deploying github repository to heoku - swift

Question

Trying to deploy this repository to heoku using the deploy to heroku button.
https://github.com/abdulkhaliq92/FaxServer
I have a valid app.json file:
{
"name": "FaxServer",
"scripts": {},
"env": {},
"formation": {},
"addons": [],
"buildpacks": [
{
"url": "https://github.com/kylef/heroku-buildpack-swift"
}
]
}
The following error occurs while deploying.
Downloading swift-corelibs-libdispatch (swift-4.1-RELEASE)
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 --:--:-- --:--:-- --:--:-- 1729k
Building Swift
This may take a very long time...
Building Swift failed
Check out the logfile for more information: /app/tmp/cache/swiftenv/tmp/swiftenv-build-4.1/swiftenv-build.20190214170118.272.log
You can inspect or delete the working tree at: /app/tmp/cache/swiftenv/tmp/swiftenv-build-4.1
! Push rejected, failed to compile Swift app.
! Push failed
EDIT:
Still getting the same error.
Here is the Package.swift file : https://github.com/abdulkhaliq92/FaxServer/blob/master/Package.swift