Install yarn via npm

Author: fbacall

Dockerfile

@@ -8,7 +8,7 @@ WORKDIR /code
 
 # install dependencies
 RUN apt-get update \
-    && apt-get install build-essential curl file git gnupg2 imagemagick libpq-dev libyaml-dev nodejs yarn -y \
+    && apt-get install build-essential curl file git gnupg2 imagemagick libpq-dev libyaml-dev nodejs -y \
     && apt-get clean
 
 
@@ -45,7 +45,7 @@ RUN bundle check || bundle install
 COPY package.json yarn.lock ./
 
 # install js dependencies
-RUN yarn install
+RUN npm install -g yarn
 
 # copy code
 COPY . .