Tie chromium apk update to @v3.11 instead of @edge

## Affected builder image

(e.g., `gcr.io/cloud-builders-community/yarn-puppeteer`)

## Expected Behavior
In Docker file: Pull chromium using apk @3.11. This ensures that v79 of Chromium is installed

## Actual Behavior
Chromium is pulled from @edge which is currently sporting chromium v80 which is not compatible with puppeteer v2.0.0. In the future the version number of chromium will keep changing thus causing further problems.

## Additional Info
Alpine package versions: https://pkgs.alpinelinux.org/packages?name=chromium&branch=v3.11

Redefine:
echo @v3.11 http://nl.alpinelinux.org/alpine/v3.11/community/ >> /etc/apk/repositories && \
echo @v3.11 http://nl.alpinelinux.org/alpine/v.3.11/main >> /etc/apk/repositories && \