Install yarn AND run yarn install

Author: fbacall

Dockerfile

@@ -11,6 +11,8 @@ RUN apt-get update \
     && apt-get install build-essential curl file git gnupg2 imagemagick libpq-dev libyaml-dev nodejs npm -y \
     && apt-get clean
 
+# install yarn to manage JS dependencies
+RUN npm install -g yarn
 
 # install supercronic - a cron alternative
 ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.12/supercronic-linux-amd64 \
@@ -45,7 +47,7 @@ RUN bundle check || bundle install
 COPY package.json yarn.lock ./
 
 # install js dependencies
-RUN npm install -g yarn
+RUN yarn install
 
 # copy code
 COPY . .