Causes build scripts to fail immediately if a single command fails. (#23)

src/common/thirdparty/build-redis.sh

@@ -1,3 +1,8 @@
+#!/usr/bin/env bash
+
+# Cause the script to exit if a single command fails.
+set -e
+
 if [ ! -f redis-3.2.3/src/redis-server ]; then
   wget http://download.redis.io/releases/redis-3.2.3.tar.gz
   tar xvfz redis-3.2.3.tar.gz