Install jemalloc via apt package and configure ruby to use transparently

See docker-library/ruby#182 for more details.

Dockerfile

@@ -5,10 +5,12 @@ LABEL maintainer Travis CI GmbH <support+travis-api-docker-images@travis-ci.com>
 # packages required for bundle install
 RUN ( \
    apt-get update ; \
-   apt-get install -y --no-install-recommends git make gcc g++ libpq-dev \
+   apt-get install -y --no-install-recommends git make gcc g++ libpq-dev libjemalloc-dev \
    && rm -rf /var/lib/apt/lists/* \
 )
 
+ENV LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2
+
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN bundle config --global frozen 1
 RUN bundle config set deployment 'true'

Procfile

@@ -1,3 +1,3 @@
 web: ./script/server-buildpacks
-console: jemalloc.sh bundle exec ./script/console
-cron: jemalloc.sh bundle exec ./bin/cron
+console: bundle exec ./script/console
+cron: bundle exec ./bin/cron

script/server

@@ -25,9 +25,9 @@ cmd="unicorn config.ru -E $RACK_ENV -c config/unicorn.rb"
 [[ $RACK_ENV == "development" ]] && cmd="rerun -b -- $cmd"
 
 if [ -z "$DYNO" ]; then
-  cmd="jemalloc.sh bundle exec $cmd"
+  cmd="bundle exec $cmd"
 else
-  cmd="jemalloc.sh bin/start-nginx $cmd"
+  cmd="bin/start-nginx $cmd"
 fi
 
 exec $cmd