Fails with flutter not found

[paines]

I wanted to check out how I would devleop an iOS App with Flutter and Linux. SO I cloned the repo and executed"

docker build -t codemagic-demo .

This will run for a while pulling Android SDKs and such, doing apt-get command etc, and then fail in the end with

....
...
..
Setting up lcov (1.13-3) ...
Processing triggers for libc-bin (2.27-3ubuntu1.4) ...
Cloning into 'flutter'...
/bin/sh: 1: /flutter/bin/flutter: not found
The command '/bin/sh -c apt-get update &&     apt-get install -y lcov git-core curl unzip &&     git clone https://github.com/flutter/flutter.git &&     /flutter/bin/flutter doctor &&     apt-get remove -y curl unzip &&     apt autoremove -y &&     rm -rf /var/lib/apt/lists/*' returned a non-zero code: 127