Optimize ShellCheck installation in Docker image

Use pre-built static release binary instead of building ShellCheck from
the source code, this change would save disk space, time, and much
computing resources.

Dockerfile

@@ -14,6 +14,9 @@ MAINTAINER Peter Dave Hello <hsu@peterdavehello.org>
 # Prevent dialog during apt install
 ENV DEBIAN_FRONTEND noninteractive
 
+# ShellCheck version
+ENV SHELLCHECK_VERSION=0.4.7
+
 # Pick a Ubuntu apt mirror site for better speed
 # ref: https://launchpad.net/ubuntu/+archivemirrors
 ENV UBUNTU_APT_SITE ubuntu.cs.utah.edu
@@ -49,14 +52,22 @@ RUN apt update         && \
         realpath              \
         zsh                   \
         ksh                   \
-        ghc                   \
         gcc-4.8               \
         g++-4.8               \
-        cabal-install         \
+        xz-utils              \
         build-essential       \
         bash-completion       && \
     apt-get clean
 
+# ShellCheck with Ubuntu 14.04 container workaround
+RUN wget https://storage.googleapis.com/shellcheck/shellcheck-v$SHELLCHECK_VERSION.linux.x86_64.tar.xz -O- | \
+    tar xJvf - shellcheck-v$SHELLCHECK_VERSION/shellcheck          && \
+    mv shellcheck-v$SHELLCHECK_VERSION/shellcheck /bin             && \
+    rmdir shellcheck-v$SHELLCHECK_VERSION                          && \
+    touch /tmp/libc.so.6                                           && \
+    echo "alias shellcheck='LD_LIBRARY_PATH=/tmp /bin/shellcheck'" >> /etc/bash.bashrc
+RUN LD_LIBRARY_PATH=/tmp shellcheck -V
+
 # Set locale
 RUN locale-gen en_US.UTF-8
 
@@ -68,7 +79,6 @@ RUN dpkg -s dash | grep ^Version | awk '{print $2}'
 RUN git --version
 RUN curl --version
 RUN wget --version
-RUN cabal --version
 
 # Add user "nvm" as non-root user
 RUN useradd -ms /bin/bash nvm
@@ -79,12 +89,6 @@ RUN echo 'nvm ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers
 # Switch to user "nvm" from now
 USER nvm
 
-# Shellcheck
-RUN cabal update
-RUN cabal install ShellCheck
-RUN ~/.cabal/bin/shellcheck --version
-RUN echo 'export PATH="~/.cabal/bin/:${PATH}"'                                >> $HOME/.bashrc
-
 # nvm
 COPY . /home/nvm/.nvm/
 RUN sudo chown nvm:nvm -R $HOME/.nvm