Firstly, thank for this tutorial. I clone this repo and test it but I got error. Do you help me?
Sending build context to Docker daemon 66.56kB
Step 1/10 : FROM dlang2/dmd-ubuntu
---> 5b791b030472
Step 2/10 : RUN mkdir -p /app
---> Using cache
---> 1c27e8f59a8f
Step 3/10 : WORKDIR /app
---> Using cache
---> 6d2f3ef3cd12
Step 4/10 : COPY . /app/
---> Using cache
---> 18293adf32d9
Step 5/10 : RUN apt-get install libssl-dev libevent-dev -y
---> Using cache
---> e959a9f6b831
Step 6/10 : RUN useradd --user-group --create-home --shell /bin/false app
---> Using cache
---> 333e9bb061f9
Step 7/10 : USER app
---> Using cache
---> 4f9ea6f881e9
Step 8/10 : RUN dub build
---> Running in af6e51505ef6
Fetching libevent 2.0.2+2.0.16 (getting selected version)...
Fetching diet-ng 1.4.4 (getting selected version)...
Fetching openssl 1.1.6+1.0.1g (getting selected version)...
Fetching memutils 0.4.10 (getting selected version)...
Fetching vibe-d 0.7.32 (getting selected version)...
Fetching libasync 0.8.3 (getting selected version)...
Cannot open file `/app/dub.selections.json' in mode `wb' (Permission denied)
The command '/bin/sh -c dub build' returned a non-zero code: 2