Add yarn to base image

Add yarn to base image

diff --git a/image/base/Dockerfile b/image/base/Dockerfile
index 3ba92b4..92762e1 100644
--- a/image/base/Dockerfile
+++ b/image/base/Dockerfile
@@ -27,6 +27,8 @@ RUN curl https://apt.postgresql.org/pub/repos/apt/ACCC4CF8.asc | apt-key add -
 RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main" | \
         tee /etc/apt/sources.list.d/postgres.list
 RUN curl --silent --location https://deb.nodesource.com/setup_16.x | sudo bash -
+RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
+RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" > /etc/apt/sources.list.d/yarn.list
 RUN apt -y update
 # install these without recommends to avoid pulling in e.g.
 # X11 libraries, mailutils
@@ -52,7 +54,7 @@ RUN cd / &&\
     apt clean &&\
     rm -f /etc/apt/apt.conf.d/40proxy &&\
     locale-gen en_US &&\
-    apt install -y nodejs &&\
+    apt install -y nodejs yarn &&\
     npm install -g terser &&\
     npm install -g uglify-js
 

GitHub sha: b1e44c376a9a599bf5baff2341782bc75ef00d0a

This commit appears in #556 which was approved by eviltrout. It was merged by Falco.