Resolves ARC-99 Add jemalloc to your Ruby Docker images

.docker/Dockerfile.unstable

@@ -11,7 +11,13 @@ RUN curl https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
 RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
 
 RUN apt-get update -yqq && \
- apt-get install -yqq --no-install-recommends vim nodejs yarn
+ apt-get install -yqq --no-install-recommends \
+ nodejs yarn vim \
+ libjemalloc2 \
+ && rm -rf /var/lib/apt/lists/*
+
+ENV LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2
+
 RUN groupadd -g $GID -o $UNAME
 RUN useradd -m -d /opt/app-root -u $UID -g $GID -o -s /bin/bash $UNAME
 RUN mkdir -p /gems && chown $UID:$GID /gems