Add return to trap command

Without `return` the SIGINT is ignored (the trap arg gets executed
properly though).

bootstrap.sh

@@ -18,7 +18,7 @@ function isDebug() {
 
 function main() {
   local tmpdir="`mktemp -d -t 'macos-system'`"
-  isDebug || trap "rm -fr -- '${tmpdir}'" INT TERM EXIT
+  isDebug || trap "rm -fr -- '${tmpdir}'; return" INT TERM EXIT
   pushd -q "${tmpdir}"
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   cloneZSHLibRepo