Flutter docker image

Alpine Linux images for Flutter & Dart with useful utils and web build support.
Symlinks to dart, flutter in the folder: /opt/flutter
Rolling release update strategy every Monday.

Environment variables

• USER: root
• WORKDIR: /build
• SHELL: /bin/bash
• FLUTTER_ROOT: /opt/flutter
• PUB_CACHE: /var/tmp/.pub_cache
• ANDROID_HOME: /opt/android