docs generation: Use macos compatible copy method

hack/verify-generated-swagger-docs.sh

@@ -49,14 +49,14 @@ trap "cleanup" EXIT SIGINT
 
 cleanup
 
-mkdir -p "${_tmp}"
-cp -a -T "${DIFFROOT}" "${TMP_DIFFROOT}"
+mkdir -p "${TMP_DIFFROOT}"
+cp -a "${DIFFROOT}"/* "${TMP_DIFFROOT}/"
 
 "${KUBE_ROOT}/hack/update-generated-swagger-docs.sh"
 echo "diffing ${DIFFROOT} against freshly generated swagger type documentation"
 ret=0
 diff -Naupr -I 'Auto generated by' "${DIFFROOT}" "${TMP_DIFFROOT}" || ret=$?
-cp -a -T "${TMP_DIFFROOT}" "${DIFFROOT}"
+cp -a "${TMP_DIFFROOT}"/* "${DIFFROOT}/"
 if [[ $ret -eq 0 ]]
 then
   echo "${DIFFROOT} up to date."