Made string removal in root domain detection posix compliant

dnsapi/dns_mijn_host.sh

@@ -147,7 +147,7 @@ _get_root() {
   for rootDomain in $rootDomains; do
     if _contains "$domain" "$rootDomain"; then
       _domain="$rootDomain"
-      _sub_domain=$(printf '%s\n' "${domain//."$rootDomain"/}")
+      _sub_domain=$(echo "$domain" | sed "s/$rootDomain//g")
       return 0
     fi
   done