tools/ci.sh: Fix missing set -e when run as a script.

This is needed to correctly stop after an error in a CI step when running
`ci.sh` as a script.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

tools/ci.sh

@@ -1011,6 +1011,7 @@ function _ci_main {
             _ci_help
         ;;
         (*)
+            set -e
             cd $(dirname "$0")/..
             while [ $# -ne 0 ]; do
                 ci_$1