update sc

Signed-off-by: Jess Frazelle <acidburn@google.com>

shellcheck/Dockerfile

@@ -1,6 +1,11 @@
 FROM haskell
 MAINTAINER Jessie Frazelle <jess@linux.com>
 
+RUN apt-get update && apt-get install -y \
+	file \
+	--no-install-recommends \
+	&& rm -rf /var/lib/apt/lists/*
+
 RUN cabal update && cabal install shellcheck
 
 CMD ["shellcheck"]