Failures in script should cause script to exit immediately

[jtrupiano]

By issuing a "set -e" call at the top of the script, it will cause the entire script to exit immediately if any of the commands within the script return non-0 exit status codes.

This should aid us as a community in keeping the script up to date. Currently, the script marches on and since there are thousands of lines of output, it can be hard to detect.

This commit corrects this: http://github.com/jtrupiano/magick-installer/commit/4bbe09b7f197a05be6eb3b2971acae1c3321bbeb