ensure specified version of node is installed

docker_configs/api.Dockerfile

@@ -4,7 +4,8 @@ RUN sh -c 'VERSION_CODENAME=stretch; . /etc/os-release; echo "deb http://apt.pos
 RUN apt-get update -qq && apt-get install -y build-essential libpq-dev \
   postgresql postgresql-contrib
 RUN     curl -sL https://deb.nodesource.com/setup_8.x | bash -
-RUN     apt-get install -y nodejs npm
+RUN sh -c 'echo "\nPackage: *\nPin: origin deb.nodesource.com\nPin-Priority: 700\n" >> /etc/apt/preferences'
+RUN     apt-get install -y nodejs
 RUN     mkdir /farmbot
 WORKDIR /farmbot
 ENV     BUNDLE_PATH=/bundle BUNDLE_BIN=/bundle/bin GEM_HOME=/bundle