Make install script safer
Make install script safer

Call `set -e` to make the script exit if any command fails and `set -u`
to treat unset variables as an error.

anishathalye/dotbot,bchretien/dotbot,StijnRuts/dotbot,bchretien/dotbot,StijnRuts/dotbot,pulgalipe/dotbot,pulgalipe/dotbot,imattman/dotbot,imattman/dotbot,anishathalye/dotbot,bchretien/dotbot,pulgalipe/dotbot,imattman/dotbot,StijnRuts/dotbot