Upgrade Dockerfile to use official image

Per docker-library/official-images#3273

Dockerfile

@@ -1,34 +1,4 @@
-FROM debian:jessie
-
-ENV RUST_VERSION=1.19.0
-ENV RUST_TARGET=x86_64-unknown-linux-gnu
-
-RUN \
-  # Install tools needed from the package manager
-  apt-get update && \
-  DEBIAN_FRONTEND=noninteractive \
-  apt-get install -y \
-    ca-certificates \
-    curl \
-    build-essential \
-    gcc && \
-
-  # Use curl to download and install rust
-  curl \
-    -sO \
-    https://static.rust-lang.org/dist/rust-$RUST_VERSION-$RUST_TARGET.tar.gz \
-    && \
-  tar -xzf rust-$RUST_VERSION-$RUST_TARGET.tar.gz && \
-  ./rust-$RUST_VERSION-$RUST_TARGET/install.sh --without=rust-docs && \
-
-  # Cleanup by removing files and utilities that are no longer needed
-  DEBIAN_FRONTEND=noninteractive apt-get remove --purge -y curl && \
-  rm -rf \
-    ./rust-$RUST_VERSION-$RUST_TARGET \
-    rust-$RUST_VERSION-$RUST_TARGET.tar.gz \
-    /var/lib/apt/lists/* \
-    /tmp/* \
-    /var/tmp/*
+FROM rust
 
 # Creating a directory to work from
 RUN mkdir -p /usr/src/app